CODEWITHSUNDEEP
javascriptjslint
puk
puk

Reputation: 16792

Should var be used when variable is already a parameter (Javascript)

I have a function like so

function foo(x){
    if (typeof x === 'undefined'){
        var x = 123;
    }
}

is the var statement necessary? JSlint complains that variable x hides argument (probably b/c I am defining a variable in the scope of the if statement.

Upvotes: 2

Views: 476

Answers (2)

Tom
Tom

Reputation: 5201

The var is not necessary, and in fact it is a mistake. You should use var to declare a new variable. Once the function has an argument x it is declared - whether it is passed a value or not.

By the way, in such cases when you know the variable is declared but just don't know whether it's been assigned a value or not, you can write x === undefined - using typeof and a string comparison is not necessary.

Upvotes: 4

JaredPar
JaredPar

Reputation: 755259

No var is not needed here and it's in fact very misleading. The var modifier is used to scope a value to the current function scope. Hence it's most useful at the top of the method or at worst on the first usage of the value. Parameters are always scoped to the current function hence it has no value.

Using it for subsequent usages suggests it's the first use / declaration of the value. This can be misleading to future developers.

Upvotes: 4

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