why do we use const in for...of loops in javascript?

Question

I am wondering why we use const in javascript for...of loops. Every example I see using for...of loops use const while declaring the variable. For example:

for (const item of array) {
    // do something
}

Is there any reason we don't use var like this?

for (var item of array) {
    // do something
}

Thanks

score 2 · Accepted Answer · answered Jul 03 '20 at 17:16

2

var will load the variable into the global scope, whereas let and const will declare it in the lexical scope:

const test = [1, 2, 3];

// lexical
for (let testItem of test) {
    console.log(window.testItem);
}

// global
for (var testItem of test) {
    console.log(window.testItem);
}

answered Jul 03 '20 at 17:16

Lewis

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Bu lexical scope do you mean the scope contained within the curly brackets? – I_keep_getting_downvoted Jul 03 '20 at 17:21
1

@I_keep_getting_downvoted Exactly. `let` and `const` basically declare a "temporary" variable that is invisible to anything outside of that `for ... of` loop, but `var` will declare it as a regular global variable, which you can access at `window.testItem`. – Lewis Jul 03 '20 at 17:24
Thanks. The question has been closed before I got to accept your answer. I don't know if I will be able to do so. – I_keep_getting_downvoted Jul 03 '20 at 17:25
@I_keep_getting_downvoted No worries. I appreciate it. – Lewis Jul 03 '20 at 17:28

why do we use const in for...of loops in javascript?

1 Answers1