0 == false // true '' == false // true null == undefined // true [] == '' // true (both become empty string) [] == 0 // true Always prefer === (no coercion), except when checking null == undefined . 7. Asynchronous Weirdness: Event Loop The weird part: JS is single-threaded but can handle async tasks.
typeof null; // 'object' (bug in JS) typeof function(){}; // 'function' (but not a separate type) [] instanceof Array; // true [] instanceof Object; // true (arrays are objects) false , 0 , '' (empty string), null , undefined , NaN , -0 , 0n understanding javascript the weird part parts
const obj = name: 'Alice', greet() console.log(this.name); ; const greetFn = obj.greet; greetFn(); // undefined (default binding, not implicit) Fix: use arrow functions (lexical this ) or .bind() . The weird part: A function “remembers” its lexical scope even when executed outside it. 0 == false // true '' == false
function Dog(name) this.name = name; Dog.prototype.bark = function() return 'woof'; ; const d = new Dog('Rex'); d.bark(); // 'woof' Weird parts: typeof null; // 'object' (bug in JS) typeof