Javascript var declaration hoisting

Introduction

When using var, the following code is possible.

The variables declared using var keyword are hoisted to the top of the function scope: 

function myMethod() { 
   console.log(age); 
   var age = 12; 
} 
myMethod();  // undefined

This does not throw an error because the Javascript treats it like this: 

function myMethod() { 
   var age; 
   console.log(age); 
   age = 12; 
} 
myMethod();  // undefined

This is called "hoisting" where the interpreter pulls all variable declarations to the top of its scope.

var also allows us to use redundant var declarations: 

function myMethod() { 
   var age = 16; 
   var age = 26; 
   var age = 36;  
   console.log(age); 
} 
myMethod();  // 36



PreviousNext

Related