JavaScript block scope, methods for redeclaring variables
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
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