Ngày tháng trong JavaScript

Thứ Hai, 24/08/2020

Tram Ho

1. Khởi tạo Date Object

Mặc dù chỉ gọi là Date (ngày), nhưng nó đã bao gồm luôn các API về thời gian

// Ngày giờ hiện tại

<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

1 2	<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

// nếu truyền vào 0, chúng ta có giá trị Jan 1st 1970 (UTC)

<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

1 2	<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

UNIX timestamp là giá trị bằng số ( tính đến giây) của Date

LƯU Ý: UNIX timestamp tính theo giây. Date của JavaScript tính theo milli giây

Nếu có giá trị UNIX timestamp, khởi tạo một Date Object bằng cách nhân với 1000

<span class="token keyword">const</span> timestamp <span class="token operator">=</span> <span class="token number">1530826362</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span>timestamp <span class="token operator">*</span> <span class="token number">1000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

const timestamp = 1530826362;

new Date(timestamp * 1000);

Nếu truyền vào một string, thay vì number, gọi Date(string) sẽ parse giá trị đó, hay ho là ở chỗ nó tự đoán mò xem string truyền vào đang theo định dạng nào.

<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020-07-21"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020-07"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//July 1st 2020, 00:00:00</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Jan 1st 2020, 00:00:00</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"07/22/2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020/07/22"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020/7/22"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020-07-22 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020-07-22T07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"25 March 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"25 Mar 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"25 March, 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"March 25, 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"March 25 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"March 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Mar 1st 2020, 00:00:00</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020 March"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Mar 1st 2020, 00:00:00</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020 MARCH"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Mar 1st 2020, 00:00:00</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"2020 march"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Mar 1st 2020, 00:00:00</span>

new Date("2020-07-21");

new Date("2020-07"); //July 1st 2020, 00:00:00

new Date("2020"); //Jan 1st 2020, 00:00:00

new Date("07/22/2020");

new Date("2020/07/22");

new Date("2020/7/22");

new Date("July 22, 2020");

new Date("July 22, 2020 07:22:13");

new Date("2020-07-22 07:22:13");

new Date("2020-07-22T07:22:13");

new Date("25 March 2020");

new Date("25 Mar 2020");

new Date("25 March, 2020");

new Date("March 25, 2020");

new Date("March 25 2020");

new Date("March 2020"); //Mar 1st 2020, 00:00:00

new Date("2020 March"); //Mar 1st 2020, 00:00:00

new Date("2020 MARCH"); //Mar 1st 2020, 00:00:00

new Date("2020 march"); //Mar 1st 2020, 00:00:00

Việc này có một nguy hiểm, thứ tự ngày tháng có thể không đúng như chúng ta mong đợi.

Tốt nhất là cứ theo chuẩn quốc tế ISO 8601, string dạng thế này

<span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">YYYY-MM-DDTHH:mm:ss:sssZ</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>

1 2	<span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">YYYY-MM-DDTHH:mm:ss:sssZ</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>

Điểm lưu ý duy nhất của string này là chữ Z cuối cùng, nó đại diện cho UTC, nếu không có, tức là đang dùng giờ địa phương.

Dùng Date.parse, sẽ trả về timestamp (milli giây)

Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"2020-07-22"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"2020-07"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//July 1st 2020, 00:00:00</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//Jan 1st 2020, 00:00:00</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"07/22/2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"2020/07/22"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"2020/7/22"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"2020-07-22 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
Date<span class="token punctuation">.</span><span class="token function">parse</span><span class="token punctuation">(</span><span class="token string">"2020-07-22T07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Date.parse("2020-07-22");

Date.parse("2020-07"); //July 1st 2020, 00:00:00

Date.parse("2020"); //Jan 1st 2020, 00:00:00

Date.parse("07/22/2020");

Date.parse("2020/07/22");

Date.parse("2020/7/22");

Date.parse("July 22, 2020");

Date.parse("July 22, 2020 07:22:13");

Date.parse("2020-07-22 07:22:13");

Date.parse("2020-07-22T07:22:13");

Hoặc là truyền theo dạng năm, tháng (từ 0), ngày, giờ, phút, giây, mili giây

<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token number">2020</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">,</span> <span class="token number">7</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">,</span> <span class="token number">13</span><span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token number">2020</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">22</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

new Date(2020, 6, 22, 7, 22, 13, 0);

2. Timezone – Khu vực

Khi khởi tạo một giá trị ngày giờ chúng ta có thể truyền thêm tham số timezone, nếu không muốn dùng UTC

// bằng cách thêm +HOURS

<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2018 07:22:13 +0700"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

1 2	<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2018 07:22:13 +0700"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

// bằng cách thêm tên , ICT gồm Campuchia, Lào, Thái Lan, Việt Nam

<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13 (ICT)"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

1 2	<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13 (ICT)"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Nếu truyền sai giá trị timezone, javascript sẽ dùng UTC, không quăng lỗi. Nếu giá trị date đưa vào sai, xảy ra lỗi ‘Invalid Date’

3. Convert và Format kiểu Date

Với một Date object, chúng ta có khá nhiều lựa chọn để chuyển giá trị Date => string

<span class="token keyword">const</span> date <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

date<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// "Sun Jul 22 2020 07:22:13 GMT+0200 (Central European Summer Time)"</span>
date<span class="token punctuation">.</span><span class="token function">toTimeString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//"07:22:13 GMT+0200 (Central European Summer Time)"</span>
date<span class="token punctuation">.</span><span class="token function">toUTCString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//"Sun, 22 Jul 2020 05:22:13 GMT"</span>
date<span class="token punctuation">.</span><span class="token function">toDateString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//"Sun Jul 22 2020"</span>
date<span class="token punctuation">.</span><span class="token function">toISOString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//"2018-07-22T05:22:13.000Z" (ISO 8601 format)</span>
date<span class="token punctuation">.</span><span class="token function">toLocaleString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//"22/07/2020, 07:22:13"</span>
date<span class="token punctuation">.</span><span class="token function">toLocaleTimeString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//"07:22:13"</span>
date<span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

const date = new Date("July 22, 2020 07:22:13");

date.toString();

// "Sun Jul 22 2020 07:22:13 GMT+0200 (Central European Summer Time)"

date.toTimeString();

//"07:22:13 GMT+0200 (Central European Summer Time)"

date.toUTCString();

//"Sun, 22 Jul 2020 05:22:13 GMT"

date.toDateString();

//"Sun Jul 22 2020"

date.toISOString();

//"2018-07-22T05:22:13.000Z" (ISO 8601 format)

date.toLocaleString();

//"22/07/2020, 07:22:13"

date.toLocaleTimeString();

//"07:22:13"

date.getTime();

4.Các phương thức của Date Object để lấy giá trị

<span class="token keyword">const</span> date <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2018 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

date<span class="token punctuation">.</span><span class="token function">getDate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//22</span>
date<span class="token punctuation">.</span><span class="token function">getDay</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//0 (0 là chủ nhật, 1 là thứ 2..)</span>
date<span class="token punctuation">.</span><span class="token function">getFullYear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//2018</span>
date<span class="token punctuation">.</span><span class="token function">getMonth</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//6 (Bắt đầu từ 0)</span>
date<span class="token punctuation">.</span><span class="token function">getHours</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//7</span>
date<span class="token punctuation">.</span><span class="token function">getMinutes</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//22</span>
date<span class="token punctuation">.</span><span class="token function">getSeconds</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//13</span>
date<span class="token punctuation">.</span><span class="token function">getMilliseconds</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//0 (không xác định)</span>
date<span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//1532236933000</span>
date<span class="token punctuation">.</span><span class="token function">getTimezoneOffset</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//-120 (Tùy theo khu vực và vùng miền).</span>

const date = new Date("July 22, 2018 07:22:13");

date.getDate(); //22

date.getDay();

//0 (0 là chủ nhật, 1 là thứ 2..)

date.getFullYear(); //2018

date.getMonth(); //6 (Bắt đầu từ 0)

date.getHours(); //7

date.getMinutes(); //22

date.getSeconds(); //13

date.getMilliseconds(); //0 (không xác định)

date.getTimezoneOffset();

//-120 (Tùy theo khu vực và vùng miền).

Các phương thức trên sẽ có thêm phiên bản UTC, trả về giá trị UTC không phụ thuộc vào giá trị timezone hiện tại

date<span class="token punctuation">.</span><span class="token function">getUTCDate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//22</span>
date<span class="token punctuation">.</span><span class="token function">getUTCDay</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//0 (0 means sunday, 1 means monday..)</span>
date<span class="token punctuation">.</span><span class="token function">getUTCFullYear</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//2018</span>
date<span class="token punctuation">.</span><span class="token function">getUTCMonth</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//6 (starts from 0)</span>
date<span class="token punctuation">.</span><span class="token function">getUTCHours</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//5 (not 7 like above)</span>
date<span class="token punctuation">.</span><span class="token function">getUTCMinutes</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//22</span>
date<span class="token punctuation">.</span><span class="token function">getUTCSeconds</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//13</span>
date<span class="token punctuation">.</span><span class="token function">getUTCMilliseconds</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//0 (not specified)</span>

date.getUTCDate(); //22

date.getUTCDay(); //0 (0 means sunday, 1 means monday..)

date.getUTCFullYear(); //2018

date.getUTCMonth(); //6 (starts from 0)

date.getUTCHours(); //5 (not 7 like above)

date.getUTCMinutes(); //22

date.getUTCSeconds(); //13

date.getUTCMilliseconds(); //0 (not specified)

5. Thay đổi giá trị

Các phương thức để cập nhập lại giá trị của Date

<span class="token keyword">const</span> date <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

date<span class="token punctuation">.</span><span class="token function">setDate</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setDay</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setFullYear</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//note: đừng dùng setYear(), bỏ rồi</span>
date<span class="token punctuation">.</span><span class="token function">setMonth</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setHours</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setMinutes</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setSeconds</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setMilliseconds</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setTime</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setTimezoneOffset</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>

date.setDate(newValue);

date.setDay(newValue);

date.setFullYear(newValue); //note: đừng dùng setYear(), bỏ rồi

date.setMonth(newValue);

date.setHours(newValue);

date.setMinutes(newValue);

date.setSeconds(newValue);

date.setMilliseconds(newValue);

date.setTime(newValue);

date.setTimezoneOffset(newValue);

Lưu ý, nếu ta dùng date.setHours(48) sẽ vẫn ok, nó sẽ tự động cộng lên thành một ngày mới, tương tự cho setMinutes, setSeconds

Với setHours() chúng ta có thể truyền tham số kiểu setHours(0,0,0,0) để cập nhập giờ-phút-giây-mili giây.

Phiên bản UTC

<span class="token keyword">const</span> date <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

date<span class="token punctuation">.</span><span class="token function">setUTCDate</span><span class="token punctuation">(</span>newalue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setUTCDay</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setUTCFullYear</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setUTCMonth</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setUTCHours</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setUTCMinutes</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setUTCSeconds</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>
date<span class="token punctuation">.</span><span class="token function">setUTCMilliseconds</span><span class="token punctuation">(</span>newValue<span class="token punctuation">)</span><span class="token punctuation">;</span>

date.setUTCDate(newalue);

date.setUTCDay(newValue);

date.setUTCFullYear(newValue);

date.setUTCMonth(newValue);

date.setUTCHours(newValue);

date.setUTCMinutes(newValue);

date.setUTCSeconds(newValue);

date.setUTCMilliseconds(newValue);

6. Lấy giá trị timestamp hiện tại

Nếu muốn lấy timestamp hiện tại (mili giây)

Date<span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">// tương tự như viết</span>
<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

Date.now();

// tương tự như viết

new Date().getTime();

7. Javascript tự động cộng thêm giá trị ngày giờ

Nếu chúng ta đưa vào giá trị ngày lớn hơn 31, javascript sẽ cộng lên thành tháng tiếp theo, chứ không báo lỗi (không rõ là nên vui hay buồn với tính năng này)

<span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token number">2018</span><span class="token punctuation">,</span> <span class="token number">6</span><span class="token punctuation">,</span> <span class="token number">40</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token comment">//Thu Aug 09 2020 00:00:00 GMT+0200</span>

new Date(2018, 6, 40);

//Thu Aug 09 2020 00:00:00 GMT+0200

8. Định dạng ngày giờ theo vùng miền

Nếu trình duyệt hỗ trợ Intl, ta có thể sử dụng để bản địa hóa các giá trị number, string, currencies, date

<span class="token comment">// "12/22/2020"</span>
<span class="token keyword">const</span> date <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">new</span> <span class="token class-name">Intl<span class="token punctuation">.</span>DateTimeFormat</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">format</span><span class="token punctuation">(</span>date<span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token comment">// định dạng kiểu Mỹ</span>
<span class="token keyword">new</span> <span class="token class-name">Intl<span class="token punctuation">.</span>DateTimeFormat</span><span class="token punctuation">(</span><span class="token string">"en-US"</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">format</span><span class="token punctuation">(</span>date<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//"7/22/2020"</span>

// "12/22/2020"

new Intl.DateTimeFormat().format(date);

// định dạng kiểu Mỹ

new Intl.DateTimeFormat("en-US").format(date); //"7/22/2020"

<span class="token comment">// đưa thêm option để customize lại output</span>
<span class="token keyword">const</span> options <span class="token operator">=</span> <span class="token punctuation">{</span>
  year<span class="token operator">:</span> <span class="token string">"numeric"</span><span class="token punctuation">,</span>
  month<span class="token operator">:</span> <span class="token string">"numeric"</span><span class="token punctuation">,</span>
  day<span class="token operator">:</span> <span class="token string">"numeric"</span><span class="token punctuation">,</span>
  hour<span class="token operator">:</span> <span class="token string">"numeric"</span><span class="token punctuation">,</span>
  minute<span class="token operator">:</span> <span class="token string">"numeric"</span><span class="token punctuation">,</span>
  second<span class="token operator">:</span> <span class="token string">"numeric"</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">new</span> <span class="token class-name">Intl<span class="token punctuation">.</span>DateTimeFormat</span><span class="token punctuation">(</span><span class="token string">"en-US"</span><span class="token punctuation">,</span> options<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">format</span><span class="token punctuation">(</span>date<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//"7/22/2020, 7:22:13 AM"</span>
<span class="token keyword">new</span> <span class="token class-name">Intl<span class="token punctuation">.</span>DateTimeFormat</span><span class="token punctuation">(</span><span class="token string">"it-IT"</span><span class="token punctuation">,</span> options2<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">format</span><span class="token punctuation">(</span>date<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">//"22/7/2020, 07:22:13"</span>

// đưa thêm option để customize lại output

const options = {

year: "numeric",

month: "numeric",

day: "numeric",

hour: "numeric",

minute: "numeric",

second: "numeric"

};

new Intl.DateTimeFormat("en-US", options).format(date); //"7/22/2020, 7:22:13 AM"

new Intl.DateTimeFormat("it-IT", options2).format(date); //"22/7/2020, 07:22:13"

9. So sánh 2 giá trị ngày giờ

Sử dụng Date.getTime() để tính toán sự giá trị ngày tháng, chính xác tới mili giây nhé

<span class="token keyword">const</span> date1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 10, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> date2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 22, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> diff <span class="token operator">=</span> date2<span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-</span> date1<span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

const date1 = new Date("July 10, 2020 07:22:13");

const date2 = new Date("July 22, 2020 07:22:13");

const diff = date2.getTime() - date1.getTime();

Kiểm tra 2 giá trị Date có bằng nhau không

<span class="token keyword">const</span> date1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 10, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> date2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Date</span><span class="token punctuation">(</span><span class="token string">"July 10, 2020 07:22:13"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>date2<span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">===</span> date1<span class="token punctuation">.</span><span class="token function">getTime</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token comment">//dates are equal</span>
<span class="token punctuation">}</span>

const date2 = new Date("July 10, 2020 07:22:13");

if (date2.getTime() === date1.getTime()) {

//dates are equal

}

Lưu ý là đang so sánh đến mili giây, nên nếu so sánh 2 giá trị July 10, 2018 07:22:13 và July 10, 2018 thì nó sẽ không bằng nhau nhaa

Source: https://css-tricks.com/everything-you-need-to-know-about-date-in-javascript/

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Nguồn bài viết : Viblo