Hoisting - MDN Web Docs Glossary: Definitions of Web-related terms | MDN

JavaScript Hoisting refers to the process whereby the interpreter appears to move the declaration of functions, variables or classes to the top of their Variable Scope, prior to execution of the code.

An important difference between function declarations and class declarations is that while functions can be called in code that appears before they are defined, classes must be defined before they can be constructed. Code like the following will throw a ReferenceError:

Function hoisting

One of the advantages of hoisting is that it lets you use a function before you declare it in your code.

function catName(name) {
  console.log(`My cat's name is ${name}`);
The result of the code above is: "My cat's name is Tiger"


Function expressions and class expressions are not hoisted.

notHoisted(); // TypeError: notHoisted is not a function
let notHoisted = function () {
const p = new Rectangle(); // ReferenceError
class Rectangle {}