How to reset variables in JavaScript
This article introduces the knowledge of "how to reset variables in JavaScript". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!
Reset variable
Variables declared with the var keyword can be modified anywhere:
Case study
Var x = 2; / / legal
Var x = 3; / / legal
X = 4; / / legal
In the same scope or block-level scope, you cannot use the const keyword to reset variables declared by the var and let keywords:
Var x = 2; / / legal
Const x = 2; / / illegal
{
Let x = 2; / / legal
Const x = 2; / / illegal
}
You cannot use the const keyword to reset variables declared by the const keyword in the same scope or block-level scope:
Const x = 2; / / legal
Const x = 3; / / illegal
X = 3; / / illegal
Var x = 3; / / illegal
Let x = 3; / / illegal
{
Const x = 2; / / legal
Const x = 3; / / illegal
X = 3; / / illegal
Var x = 3; / / illegal
Let x = 3; / / illegal
}
The const keyword can redeclare assignments in different scopes or in different block-level scopes:
Const x = 2; / / legal
{
Const x = 3; / / legal
}
{
Const x = 4; / / legal
}
Variable lifting
Variables defined by the JavaScript var keyword can be declared after use, that is, variables can be used first and then declared (JavaScript variable promotion).
Case study
CarName = "Volvo"; / / you can use the carName variable here
Var carName
Variables defined by the const keyword cannot be declared after use, that is, variables need to be declared before they are used.
CarName = "Volvo"; / / you cannot use the carName variable here
Const carName = "Volvo"
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