Pinned Loading

1. Modern JavaScript in React Documenta... Modern JavaScript in React Documentation

   1

   If you haven’t worked with JavaScript in the last few years, these three points should give you enough knowledge to feel comfortable reading the React documentation:

   2

   3

   * We define variables with [`let`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let) and [`const`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const) statements. For the purposes of the React documentation, you can consider them equivalent to [`var`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/var).

   4

   * We use the `class` keyword to define [JavaScript classes](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes). There are two things worth remembering about them. Firstly, unlike with objects, you *don't* need to put commas between class method definitions. Secondly, unlike many other languages with classes, in JavaScript the value of `this` in a method [depends on how it is called](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Classes#Boxing_with_prototype_and_static_methods).

   5

   * We sometimes use `=>` to define ["arrow functions"](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions). They're like regular functions, but shorter. For example, `x => x * 2` is roughly equivalent to `function(x) { return x * 2; }`. Importantly, arrow functions [don't have their own `this` value](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions#No_separate_this) so they're handy when you want to preserve the `this` value from an outer method definition.