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Function Hoisting

Medium

In plain terms

Function declarations are hoisted - they can be called before they appear in the code. Function expressions and arrow functions are not hoisted. Variable declarations are hoisted but not initializations.

What you need to know

  • •Declarations hoisted
  • •Expressions not hoisted
  • •var vs let/const

Try it yourself

Copy the code below and run it in your browser console or a code editor:

// Works - declaration hoisted
sayHi();
function sayHi() {
  console.log('Hi');
}

// Error - expression not hoisted
// sayHello();
const sayHello = function() { console.log('Hello'); };

// var is hoisted (undefined), let/const in TDZ
console.log(x);  // undefined (var)
var x = 5;
// console.log(y);  // Error - TDZ
let y = 10;

Learn more

Dive deeper with these trusted resources:

MDNjavascript.infoTutorialsPointW3Schools