New JavaScript features in ES12-2021

1. replaceAll

• syntax "<string>".replaceAll(<pattern>);
• Phương thức này trả về một chuỗi string mới đã được thay thế theo pattern.
• Example:
  
  const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?'; console.log(p.replaceAll('dog', 'monkey')); // Output: "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?"

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  const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';      console.log(p.replaceAll('dog', 'monkey'));      // Output:  "The quick brown fox jumps over the lazy monkey. If the monkey reacted, was it really lazy?"

• <pattern> là một string hoặc cũng có thể là một regex
  
  const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?'; const regex = /Dog/ig; console.log(p.replaceAll(regex, 'ferret')); // expected output: "The quick brown fox jumps over the lazy ferret. If the ferret reacted, was it really lazy?"

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  const p = 'The quick brown fox jumps over the lazy dog. If the dog reacted, was it really lazy?';      const regex = /Dog/ig;      console.log(p.replaceAll(regex, 'ferret'));      // expected output: "The quick brown fox jumps over the lazy ferret. If the ferret reacted, was it really lazy?"

2. Promise.any

• Promise any nhận vào 1 mảng Promise Object, và nó sẽ reslove sau khi có 1 Promise Object trong mảng resolve
• Example:
  
  const promise1 = Promise.reject(0); const promise2 = new Promise((resolve) => setTimeout(resolve, 100, 'quick')); const promise3 = new Promise((resolve) => setTimeout(resolve, 500, 'slow')); const promises = [promise1, promise2, promise3]; Promise.any(promises).then((value) => console.log(value)); // Output: "quick"

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  const promise1 = Promise.reject(0);     const promise2 = new Promise((resolve) => setTimeout(resolve, 100, 'quick'));     const promise3 = new Promise((resolve) => setTimeout(resolve, 500, 'slow'));       const promises = [promise1, promise2, promise3];       Promise.any(promises).then((value) => console.log(value));       // Output: "quick"

3. Logical Assignment Operator

• Logical Assignment Operator sẽ combine(cho phép kết hợp) giữa toán tử logic và biểu thức gán.
• Example:
  
  a ||= b // equals to a = a || (a = b) a &&= b // equals to a = a && (a = b) a ??= b // equals to a = a ?? (a = b)

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  a ||= b     // equals to     a = a || (a = b)       a &&= b     // equals to     a = a && (a = b)       a ??= b     // equals to     a = a ?? (a = b)

4. Underscores as Numeric Separator

• Example:
  
  const billion = 1_000_000_000; console.log(billion); // 1000000000 1_000_000_000 === 1000000000; // true

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  const billion = 1_000_000_000;     console.log(billion); // 1000000000       1_000_000_000 === 1000000000; // true

Refer
Javascript-es2021-you-need-to-see-these-es12-features