Introduction to Core-JS

core-js is a widely adopted JavaScript library that provides a plethora of polyfills for modern JavaScript features and standard library methods. It is essential for ensuring your JavaScript applications stay compatible with older browsers, while still utilizing the latest ECMAScript features.

Array Methods

Array.prototype.includes

  
    const includesExample = [1, 2, 3].includes(2); // true
  

Array.from

  
    const arrayFromExample = Array.from('foo'); // ['f', 'o', 'o']
  

Object Methods

Object.assign

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

Object.entries

  
    const objEntriesExample = Object.entries({ a: 1, b: 2 });
    // [['a', 1], ['b', 2]]
  

String Methods

String.prototype.startsWith

  
    const startsWithExample = 'JavaScript'.startsWith('Java'); // true
  

String.prototype.endsWith

  
    const endsWithExample = 'JavaScript'.endsWith('Script'); // true
  

Number Methods

Number.isInteger

  
    const isIntegerExample = Number.isInteger(123); // true
  

Promise Methods

Promise.all

  
    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']
    });
  

App Example with Core-JS

Let’s create a simple app that uses the above methods:

  
    import 'core-js/stable';
    import 'regenerator-runtime/runtime';

    // Check if an array includes a value
    const arrayCheck = [1, 2, 3].includes(2); // true

    // Convert a string to an array
    const stringToArray = Array.from('hello'); // ['h', 'e', 'l', 'l', 'o']

    // Merge objects
    const originalObj = { a: 1 };
    const newObj = Object.assign({}, originalObj, { b: 2 });

    // Check string patterns
    const startsWithHello = 'Hello World'.startsWith('Hello'); // true

    // Use multiple promises
    const promiseResult = Promise.all([
      Promise.resolve('First Promise'),
      Promise.resolve('Second Promise')
    ]).then(results => {
      console.log(results); // ['First Promise', 'Second Promise']
    });

    console.log({ arrayCheck, stringToArray, newObj, startsWithHello });
  

With core-js, you can ensure browser compatibility and leverage modern JavaScript features efficiently.

Hash: a421b0bafc79bc3423c971f06c33074e7d59ca0963bd2ff8a7e37e4c0d7ae2fe