javascript - Do I need to create a variable in a for-loop? -

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i'm new javascript, i'm sorry if question stupid. told when create for-loop, should write:

for (var = 0; < 10; i++)

but forget put var before i:

for (i = 0; < 10; i++)

and works same. need create variable i?

what's main difference between

var = 0

and

i = 0

in for-loop?

when declare variable var it's scope limited,

when don't use var variable in global scope. means can access variable anywhere.

And