Làm thế nào để chuyển đổi Callback thành Promise trong JavaScript/Node.js?

Thứ Sáu, 28/10/2022

Tram Ho

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Callback : Về JavaScript thì callback là một hàm được truyền dưới dạng tham số cho một hàm khác. Hàm thực thi ngay khi kết quả của hàm gọi sẵn sàng. Nói cách đơn giản, nó xử lý các yêu cầu không đồng bộ của JavaScript.

Ví dụ tốt nhất để chứng minh điều này là sử dụng một hàm setTimeout () nhận một hàm callback và trì hoãn việc thực thi code. Ngay sau khi hết thời gian đặt cho hàm, hàm callback sẽ thực thi.

<span class="token keyword">var</span> <span class="token function-variable function">callback</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"Hello! GeeksforGeeks"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token function">setTimeout</span><span class="token punctuation">(</span>callback<span class="token punctuation">,</span> <span class="token number">2000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

var callback = () => {

console.log("Hello! GeeksforGeeks");

};

setTimeout(callback, 2000);

Đầu ra:

Hello! GeeksforGeeks

Promise: Nó rất giống với các lệnh callback đang hoạt động. Tuy nhiên, lợi thế của việc sử dụng Promises là cải thiện khả năng đọc code vì nó giúp chúng ta thoát khỏi callback hell.
Promise có bốn state:

Pending: Promise vẫn chưa hoàn thành. Không thành công cũng chưa thất bại.
Fulfilled: Promise kết thúc thành công.
Reject: Promise kết thúc bằng một lỗi.
Settled: Promise có lỗi hoặc đã thành công.

Chuyển một lệnh callback hiện có thành Promise:

<span class="token keyword">var</span> <span class="token function-variable function">callback</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">err<span class="token punctuation">,</span> success</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>err<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"Geek is very sad!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"Geek is optimistic, "</span> <span class="token operator">+</span> <span class="token string">"thus becomes successful"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">var</span> <span class="token function-variable function">caller</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">status<span class="token punctuation">,</span> callback</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>status <span class="token operator">===</span> <span class="token string">"Happy"</span><span class="token punctuation">)</span> <span class="token function">callback</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> <span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token function">callback</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Error</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token function">caller</span><span class="token punctuation">(</span><span class="token string">"Happy"</span><span class="token punctuation">,</span> callback<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">caller</span><span class="token punctuation">(</span><span class="token string">"Sad"</span><span class="token punctuation">,</span> callback<span class="token punctuation">)</span><span class="token punctuation">;</span>

var callback = function (err, success) {

if (err) {

console.log("Geek is very sad!");

} else {

console.log("Geek is optimistic, " + "thus becomes successful");

}

};

var caller = function (status, callback) {

if (status === "Happy") callback(null, true);

else {

callback(new Error(), false);

}

};

caller("Happy", callback);

caller("Sad", callback);

Đầu ra:

Geek is optimistic, thus becomes successful
Geek is very sad!

Geek is optimistic, thus becomes successful

Geek is very sad!

Các bước thực hiện chuyển đổi code ở trên thành Promise:

Tạo một hàm có tên error và chèn khối code xử lý khi gặp lỗi ở trên của hàm callback vào đó.
Tạo một function có tên là success và chèn khối code xử lý khi thành công ở trên vào đó.
Sau đó, sửa đổi code caller bằng cách trả về đối tượng promise.
Sử dụng các hàm success và error theo bất kỳ cách nào sau đây.
Xem đoạn code dưới đây để hiểu rõ hơn.

<span class="token keyword">var</span> <span class="token function-variable function">error</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"Geek is very sad!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">var</span> <span class="token function-variable function">success</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"Geek is optimistic, "</span> <span class="token operator">+</span> <span class="token string">"thus becomes successful"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">var</span> <span class="token function-variable function">caller</span> <span class="token operator">=</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">status</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">Promise</span><span class="token punctuation">(</span><span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">resolve<span class="token punctuation">,</span> reject</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>status <span class="token operator">===</span> <span class="token string">"Happy"</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token function">resolve</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
      <span class="token function">reject</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token function">caller</span><span class="token punctuation">(</span><span class="token string">"Happy"</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span>success<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">catch</span><span class="token punctuation">(</span>error<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">caller</span><span class="token punctuation">(</span><span class="token string">"Sad"</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span>success<span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">catch</span><span class="token punctuation">(</span>error<span class="token punctuation">)</span><span class="token punctuation">;</span>

var error = function () {

};

var success = function () {

console.log("Geek is optimistic, " + "thus becomes successful");

};

var caller = function (status) {

return new Promise(function (resolve, reject) {

resolve();

} else {

reject();

}

});

};

caller("Happy").then(success).catch(error);

caller("Sad").then(success).catch(error);

Đầu ra:

Geek is optimistic<span class="token punctuation">,</span> thus becomes successful
Geek is very sad<span class="token operator">!</span>

Geek is optimistic, thus becomes successful

Geek is very sad!

Áp dụng chúng vào Nodejs nào.

Cài đặt Nodejs và thiết lập một ứng dụng Node đơn giản bằng cách làm theo các bước được hiển thị ở đây .

Ví dụ: Ở đây, kịch bản là chúng ta có một array sinh viên có id và tên là các value. Chúng ta cần lấy tên của sinh viên có id đã cho. Chúng ta được cung cấp một lệnh callback hiện có cần được chuyển đổi thành một promise.

<span class="token keyword">const</span> express <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">"express"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> app <span class="token operator">=</span> <span class="token function">express</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">var</span> students <span class="token operator">=</span> <span class="token punctuation">[</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">101</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek A"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">102</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek B"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">103</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek C"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">104</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek D"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">]</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> <span class="token function-variable function">callback</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">err<span class="token punctuation">,</span> student</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  <span class="token keyword">if</span> <span class="token punctuation">(</span>err<span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">Student with given id </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>err<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> not found</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token string">"Here is the student: "</span> <span class="token operator">+</span> student<span class="token punctuation">.</span>name<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> <span class="token function-variable function">findName</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">studentId<span class="token punctuation">,</span> callbackFunction</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  <span class="token keyword">let</span> student <span class="token operator">=</span> students<span class="token punctuation">.</span><span class="token function">find</span><span class="token punctuation">(</span><span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">studentValue</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> studentValue<span class="token punctuation">.</span>id <span class="token operator">==</span> studentId<span class="token punctuation">;</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

  <span class="token keyword">if</span> <span class="token punctuation">(</span><span class="token keyword">typeof</span> student <span class="token operator">===</span> <span class="token string">"undefined"</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token function">callbackFunction</span><span class="token punctuation">(</span>studentId<span class="token punctuation">,</span> <span class="token boolean">false</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
    <span class="token keyword">return</span> <span class="token function">callbackFunction</span><span class="token punctuation">(</span><span class="token keyword">null</span><span class="token punctuation">,</span> student<span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> <span class="token function-variable function">getName</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">req<span class="token punctuation">,</span> res</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  res<span class="token punctuation">.</span><span class="token function">send</span><span class="token punctuation">(</span><span class="token function">findName</span><span class="token punctuation">(</span>req<span class="token punctuation">.</span>params<span class="token punctuation">.</span>studentId<span class="token punctuation">,</span> callback<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

app<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token string">"/getName/:studentId"</span><span class="token punctuation">,</span> getName<span class="token punctuation">)</span><span class="token punctuation">;</span>

app<span class="token punctuation">.</span><span class="token function">listen</span><span class="token punctuation">(</span><span class="token number">8000</span><span class="token punctuation">,</span> <span class="token string">"localhost"</span><span class="token punctuation">,</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"Server Listening"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

const express = require("express");

const app = express();

var students = [

{

id: 101,

},

{

id: 102,

},

{

id: 103,

},

{

id: 104,

},

];

const callback = (err, student) => {

if (err) {

return `Student with given id ${err} not found`;

} else {

return "Here is the student: " + student.name;

}

};

const findName = (studentId, callbackFunction) => {

let student = students.find(function (studentValue) {

return studentValue.id == studentId;

});

if (typeof student === "undefined") {

return callbackFunction(studentId, false);

} else {

return callbackFunction(null, student);

}

};

const getName = (req, res) => {

res.send(findName(req.params.studentId, callback));

};

app.get("/getName/:studentId", getName);

app.listen(8000, "localhost", function () {

console.log("Server Listening");

});

Đầu ra:

Bây giờ, chúng ta có thể chuyển đổi hàm callback thành các promise. Tại đây, chúng ta có thể thực hiện lại các bước trước đó, tức là logic Error trong hàm failure và logic Thành công trong hàm success. Xem đoạn code dưới đây để rõ hơn.

<span class="token keyword">const</span> express <span class="token operator">=</span> <span class="token function">require</span><span class="token punctuation">(</span><span class="token string">"express"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">const</span> app <span class="token operator">=</span> <span class="token function">express</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token keyword">var</span> students <span class="token operator">=</span> <span class="token punctuation">[</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">101</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek A"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">102</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek B"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">103</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek C"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
  <span class="token punctuation">{</span>
    id<span class="token operator">:</span> <span class="token number">104</span><span class="token punctuation">,</span>
    name<span class="token operator">:</span> <span class="token string">"Geek D"</span><span class="token punctuation">,</span>
  <span class="token punctuation">}</span><span class="token punctuation">,</span>
<span class="token punctuation">]</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> <span class="token function-variable function">success</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">student</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token string">"Here is the student: "</span> <span class="token operator">+</span> student<span class="token punctuation">.</span>name<span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> <span class="token function-variable function">failure</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">fail</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token template-string"><span class="token template-punctuation string">`</span><span class="token string">Student with the given id </span><span class="token interpolation"><span class="token interpolation-punctuation punctuation">${</span>fail<span class="token interpolation-punctuation punctuation">}</span></span><span class="token string"> was not found</span><span class="token template-punctuation string">`</span></span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> <span class="token function-variable function">findName</span> <span class="token operator">=</span> <span class="token punctuation">(</span><span class="token parameter">studentId</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">Promise</span><span class="token punctuation">(</span><span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">resolve<span class="token punctuation">,</span> reject</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
    <span class="token keyword">let</span> student <span class="token operator">=</span> students<span class="token punctuation">.</span><span class="token function">find</span><span class="token punctuation">(</span><span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token parameter">studentValue</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">return</span> studentValue<span class="token punctuation">.</span>id <span class="token operator">==</span> studentId<span class="token punctuation">;</span>
    <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">if</span> <span class="token punctuation">(</span>student<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token function">resolve</span><span class="token punctuation">(</span>student<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token punctuation">{</span>
      <span class="token function">reject</span><span class="token punctuation">(</span>id<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
  <span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

<span class="token keyword">const</span> <span class="token function-variable function">getName</span> <span class="token operator">=</span> <span class="token keyword">async</span> <span class="token punctuation">(</span><span class="token parameter">req<span class="token punctuation">,</span> res</span><span class="token punctuation">)</span> <span class="token operator">=&gt;</span> <span class="token punctuation">{</span>
  <span class="token keyword">let</span> answer <span class="token operator">=</span> <span class="token keyword">await</span> <span class="token function">findName</span><span class="token punctuation">(</span>req<span class="token punctuation">.</span>params<span class="token punctuation">.</span>studentId<span class="token punctuation">)</span>
    <span class="token punctuation">.</span><span class="token function">then</span><span class="token punctuation">(</span>success<span class="token punctuation">)</span>
    <span class="token punctuation">.</span><span class="token function">catch</span><span class="token punctuation">(</span>failure<span class="token punctuation">)</span><span class="token punctuation">;</span>

  res<span class="token punctuation">.</span><span class="token function">send</span><span class="token punctuation">(</span>answer<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>

app<span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token string">"/getName/:studentId"</span><span class="token punctuation">,</span> getName<span class="token punctuation">)</span><span class="token punctuation">;</span>

app<span class="token punctuation">.</span><span class="token function">listen</span><span class="token punctuation">(</span><span class="token number">8000</span><span class="token punctuation">,</span> <span class="token string">"localhost"</span><span class="token punctuation">,</span> <span class="token keyword">function</span> <span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
  console<span class="token punctuation">.</span><span class="token function">log</span><span class="token punctuation">(</span><span class="token string">"Server Listening"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

var students = [

{

id: 101,

},

{

id: 102,

},

{

id: 103,

},

{

id: 104,

},

];

const success = (student) => {

};

const failure = (fail) => {

return `Student with the given id ${fail} was not found`;

};

const findName = (studentId) => {

return studentValue.id == studentId;

});

if (student) {

resolve(student);

} else {

reject(id);

}

});

};

const getName = async (req, res) => {

let answer = await findName(req.params.studentId)

.then(success)

.catch(failure);

res.send(answer);

};

});

Đầu ra:

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Ref

https://tuan200tokyo.blogspot.com/2022/10/blog17-lam-nao-e-chuyen-oi-mot-callback.html

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