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Introduction to JavaScript

Let 2/2

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let Does Not Allow Redeclaration

Redeclaration means declaring a variable again. As discussed in the previous chapter, we can redeclare the variable again and again with var but we cannot do that with the let keyword.


              
123

            
var number = 5;
var number = 3;
console.log(number);

But a variable declared with let does not allow redeclaration.


              
123

            
let number = 5;
let number = 3; 
console.log(number);
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A variable named country with two values Pakistan and England has been given declared for you using the let keyword but this code won’t run because let doesn’t allow redeclaration. Your task is to make changes in the below code so that we England as the output. There are two possible ways to do get the desired result.

解答

Note: Solution-2 is not much preferable.

let Does Not Allow Hoisting

As discussed in the previous chapter, let does not allow hoisting i.e. we cannot use a variable before the declaration. Variables declared with the var keyword can be accessed or used before the declaration, for example.


              
123

            
planet = 'earth';
console.log(planet);
var planet;

But let does not allow hoisting.


              
123

            
planet = 'earth';
console.log(planet);
let planet;

Summary:

  • let is the newer way to declare variables.
  • let has block scope.
  • let does not allow redeclaration.
  • let does not allow hoisting.

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セクション 3. 章 8
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