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This article mainly introduces the JavaScript block scope, re-declaration of variable method related knowledge, the content is detailed and easy to understand, the operation is simple and fast, has a certain reference value, I believe that everyone after reading this JavaScript block scope, re-declaration of variable method article will have a harvest, let's take a look.

JavaScript block scope

Variables declared by the var keyword have no block scope.

Variables declared within block {} can be accessed from outside the block.

Example

{

Var x = 10

}

/ / you can use x here

Before ES2015, JavaScript had no block scope.

Variables with block scope can be declared using the let keyword.

Variables declared within block {} cannot be accessed from outside the block:

Example

{

Let x = 10

}

/ / you cannot use x here

Redeclare variables

Redeclaring variables using the var keyword can cause problems.

Redeclaring variables in a block also redeclares variables outside the block:

Example

Var x = 10

/ / here x is 10

{

Var x = 6

/ / here x is 6

}

/ / here x is 6

Try it yourself.

Redeclaring variables using the let keyword solves this problem.

Redeclaring variables in a block does not redeclare variables outside the block:

Example

Var x = 10

/ / here x is 10

{

Let x = 6

/ / here x is 6

}

/ / here x is 10

This is the end of this article on "JavaScript block scope, methods for redeclaring variables". Thank you for reading! I believe you all have a certain understanding of the knowledge of "JavaScript block scope and the method of redeclaring variables". If you want to learn more, you are welcome to follow the industry information channel.

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