A simple metaphor I've heard used before is that a Promise in JavaScript is like ordering a cheeseburger at a fast food restaurant. When you pay for the cheeseburger, they give you a receipt with an order number on it. That receipt represents a placeholder...
There are only 4 different events that can trigger React component lifecycle methods: When a Component Mounts A component will only mount once during its lifecycle. The following 2 methods are only called once in the component's lifecycle alongside the component's render(): * componentWillMount() * render() * componentDidMount(...
Reliably testing for NaN has become much simpler (and safer) in ES6 using Number.isNaN( x ): a = "foo" * 2; b = "bar"; Number.isNaN( a ); // true Number.isNaN( b ); // false How is this different than the current isNaN( x )? We are trying to test for, and...
Javascript’s number type is based on the “IEEE 754” standard, in which it specifically uses its double-precision, 64-bit binary floating-point format. This means that some numbers really can’t be trusted to be exact. An infamous example is: 0.1 + 0.2 === 0.3;...
JavaScript strings do not have in place mutator methods like arrays do: var arr = [ 'f', 'o', 'o' ]; arr.reverse(); arr; // Array [ 'o', 'o', 'f' ]; Since strings are immutable, we need a hack to accomplish the above with a string: var str = 'bar'; str.split('')...