ES6 Methods in JavaScript

ES6 (ECMAScript 2015) introduced several new methods for working with arrays, strings, objects, and more. These methods enhance the functionality of JavaScript, making it more efficient and readable. Here’s a summary of some key ES6 methods:

1. Array Methods

Array.from(): Creates a new array from an array-like or iterable object.
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const str = 'hello';

const arr = Array.from(str); // ['h', 'e', 'l', 'l', 'o']

Array.of(): Creates a new array with the given arguments.
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const arr = Array.of(1, 2, 3); // [1, 2, 3]

Array.prototype.find(): Returns the first element in an array that satisfies the provided testing function.

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const arr = [5, 12, 8, 130, 44];

const found = arr.find(element => element > 10); // 12

Array.prototype.findIndex(): Returns the index of the first element in an array that satisfies the provided testing function.
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const arr = [5, 12, 8, 130, 44];

const index = arr.findIndex(element => element > 10); // 1

Array.prototype.includes(): Checks if an array contains a certain element, returning true or false.
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const arr = [1, 2, 3];

arr.includes(2); // true

Array.prototype.entries(): Returns an iterator object with key/value pairs for each index in the array.
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const arr = ['a', 'b', 'c'];

for (let [index, element] of arr.entries()) {

  console.log(index, element);

}

// Output: 

// 0 'a'

// 1 'b'

// 2 'c'

2. String Methods

String.prototype.includes(): Determines whether a string contains the characters of a specified string.
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const str = 'Hello, world!';

str.includes('world'); // true

String.prototype.startsWith(): Determines whether a string begins with the characters of a specified string.
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const str = 'Hello, world!';

str.startsWith('Hello'); // true

String.prototype.endsWith(): Determines whether a string ends with the characters of a specified string.
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const str = 'Hello, world!';

str.endsWith('!'); // true

String.prototype.repeat(): Repeats the string a specified number of times.
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const str = 'Hello';

str.repeat(3); // 'HelloHelloHello'

3. Object Methods

Object.assign(): Copies the values of all enumerable properties from one or more source objects to a target object.
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const target = { a: 1 };

const source = { b: 2, c: 3 };

const result = Object.assign(target, source); // { a: 1, b: 2, c: 3 }

Object.entries(): Returns an array of a given object’s own enumerable property [key, value] pairs.
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const obj = { a: 1, b: 2, c: 3 };

Object.entries(obj); // [['a', 1], ['b', 2], ['c', 3]]

Object.values(): Returns an array of a given object's own enumerable property values.
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const obj = { a: 1, b: 2, c: 3 };

Object.values(obj); // [1, 2, 3]

Object.keys(): Returns an array of a given object's own enumerable property names.
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const obj = { a: 1, b: 2, c: 3 };

Object.keys(obj); // ['a', 'b', 'c']

4. Number Methods

Number.isNaN(): Determines whether the passed value is NaN (Not-a-Number) and its type is Number.
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Number.isNaN(NaN); // true

Number.isNaN('hello'); // false

Number.isFinite(): Determines whether the passed value is a finite number.
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Number.isFinite(10); // true

Number.isFinite(Infinity); // false

5. Promise Methods

Promise.all(): Waits for all promises to be resolved or for any to be rejected.
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const promise1 = Promise.resolve(3);

const promise2 = 42;

const promise3 = new Promise((resolve, reject) => {

  setTimeout(resolve, 100, 'foo');

});

Promise.all([promise1, promise2, promise3]).then(values => {

  console.log(values); // [3, 42, 'foo']

});

Promise.race(): Returns a promise that resolves or rejects as soon as one of the promises in the array resolves or rejects.
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const promise1 = new Promise((resolve, reject) => {

  setTimeout(resolve, 500, 'one');

});

const promise2 = new Promise((resolve, reject) => {

  setTimeout(resolve, 100, 'two');

});

Promise.race([promise1, promise2]).then(value => {

  console.log(value); // 'two'

});

These methods and features significantly improve the flexibility, readability, and efficiency of JavaScript code.