Compilers and Polyfills in JavaScript

Compilers and Polyfills in JavaScript

Compilers

// Modern ES6+ code
const getProfile = username => {
  return fetch(`https://api.github.com/users/${username}`)
    .then(response => response.json())
    .then(({ data }) => ({
      name: data.name,
      location: data.location,
      company: data.company,
      blog: data.blog.includes('https') ? data.blog : null
    }))
    .catch(e => console.warn(e));
};

// Compiled ES5 code
var getProfile = function getProfile(username) {
  return fetch('<https://api.github.com/users/>' + username)
    .then(function (response) {
      return response.json();
    })
    .then(function (_ref) {
      var data = _ref.data;
      return {
        name: data.name,
        location: data.location,
        company: data.company,
        blog: data.blog.includes('https') ? data.blog : null
      };
    })
    .catch(function (e) {
      return console.warn(e);
    });
};

Polyfills

Conformance/Compatibility Tables

Example of a Compatibility Table

Importance of Compatibility Tables

Common JavaScript Compilers

Babel

• Supports modern JavaScript (ES6+) features

• Highly configurable with a large ecosystem of plugins

• Excellent community support and documentation

• Can be slower compared to other compilers

• Requires additional configuration for optimal performance

• Transpiling modern JavaScript code for compatibility with older browsers

• Projects that require extensive use of modern JavaScript features

TypeScript Compiler (tsc)

• Enforces static type checking, reducing runtime errors

• Supports modern JavaScript features

• Integrates well with many development tools and editors

• Additional learning curve due to type annotations

• May require more boilerplate code

• Large-scale applications where type safety is crucial

• Projects that can benefit from enhanced IDE support and developer tooling

Google Closure Compiler

• Highly effective at optimizing and minifying JavaScript code

• Provides polyfills for newer ECMAScript features

• Can perform dead code elimination

• More complex to set up and use compared to other compilers

• Requires annotations for advanced optimizations

• High-performance web applications

• Projects where code size and execution speed are critical

Summary

Common JavaScript Polyfills

Fetch API

// Using fetch API polyfill
fetch('<https://api.example.com/data>')
  .then(response => response.json())
  .then(data => console.log(data))
  .catch(error => console.error('Error:', error));

Promises

// Using Promise polyfill
const promise = new Promise((resolve, reject) => {
  setTimeout(() => {
    resolve('Promise resolved');
  }, 1000);
});

promise.then(result => console.log(result));

Array.prototype.includes

// Using Array.prototype.includes polyfill
const array = [1, 2, 3];
console.log(array.includes(2)); // true

Object.assign

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

console.log(returnedTarget); // { a: 1, b: 2 }

URLSearchParams

// Using URLSearchParams polyfill
const params = new URLSearchParams('?foo=1&bar=2');
console.log(params.get('foo')); // "1"

Common Tools for JavaScript Polyfills

Core-js

• Comprehensive coverage of ECMAScript features

• Modular, allowing for selective inclusion of polyfills

• Actively maintained and widely used

• Can be large if not configured properly

• Additional configuration may be needed for optimal use

• Projects that need broad ECMAScript support

• Applications targeting a wide range of older and modern browsers

Polyfill.io

• Automatically serves only the necessary polyfills

• Reduces the amount of JavaScript loaded by the user

• Easy to use with a simple URL-based API

• Relies on an external service, which may introduce latency

• Limited customization compared to local polyfill libraries

• Websites and applications with a diverse user base

• Projects where minimizing JavaScript load is crucial

Babel Polyfill

• Integrates seamlessly with Babel transpiler

• Includes a wide range of polyfills

• Simplifies setup for projects already using Babel

• Can be large if not configured properly

• May introduce additional complexity if not using Babel

• Projects already using Babel for transpiling

• Applications that need both transpiling and polyfilling

Modernizr

• Allows conditional loading of polyfills

• Provides detailed feature detection

• Lightweight and easy to integrate

• Requires additional setup to use with polyfills

• Does not provide polyfills itself

• Projects that require fine-grained control over feature detection

• Applications that need to conditionally load polyfills based on browser capabilities

ES7 Shim

• Provides support for specific ES7 features

• Easy to integrate into existing projects

• Ensures compatibility with older browsers

• Limited to features introduced in ECMAScript 2016

• May need to be used in conjunction with other polyfill libraries for broader feature support

• Projects that need to use ES7 features in older environments

• Applications requiring minimal polyfills for ECMAScript 2016 support

// Using ES7 Shim for Array.prototype.includes
const array = [1, 2, 3];
console.log(array.includes(2)); // true

// Using ES7 Shim for exponentiation operator
const base = 2;
const exponent = 3;
console.log(base ** exponent); // 8

Conclusion