How loop variable really works [duplicate]

Question

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JavaScript variables declare outside or inside loop? (13 answers)

setTimeout in for-loop does not print consecutive values [duplicate] (10 answers)

Closed 6 years ago.

Can someone explain me why var doesn't overwrite previous values inside for loop. I know that var overwrite values when is in function and then I should use let or anonymous function. Below is an simple example:

for (var a=0; a<10; a++) {
 console.log(a);
}

Output is from 0-9. But since var has function scope, in my reasoning the variable should be overwritten and output 9 times the same number(9).

Answer 1

I think I understand your question.

So, your first example. Output cannot be overwritten. It's output. Part of the name is you put it out. So it's 0, put the 0 out. Now it's 1, put the 1 out. Now it's 2, put the 2 out. And so on.

In your second example, there's a time out. So those functions don't execute until the for loop is finished. Once the for loop is finished, a = 10. Output 10. a is still 10. Output 10 again.