Javascript local variable is overriding global variable?

Question

var x = 3;

if(1==1){
    if(2==2){
        var x= 5;       
    }
}

document.write(x); // outputs 5

So I was running some tests to understand the concept of local and global scope better. I thought declaring x with keyword var creates a local variable and ignores any variable with the same name in the parent scope. By ignore, I mean how I can change the variable x without affecting the same variable in the scope above it. But apparently my understanding of the definition of js variables is wrong. could please explain why it behaves so?

You understanding is correct, but since you are inside a if and not inside a function, both of your x have the same scope — Liora Haydont
– Liora Haydont, Commented Apr 25, 2018 at 15:31
conditions with if, and loops like for or while don't create their own scope in JS — Kaddath
– Kaddath, Commented Apr 25, 2018 at 15:32

Máté Safranka · Accepted Answer · 2018-04-25 15:32:24Z

2

var declares a local variable inside a function. For block-scope local variables, use let.

var x = 3;
if(1==1){
    if(2==2){
        let x = 5;
    }
}
console.log(x); // prints 3

answered Apr 25, 2018 at 15:32

Máté Safranka

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Mamun · Accepted Answer · 2018-04-25 15:34:17Z

0

Curly braces ({...}) does not create scope for var in JavaScript. So when you declare any variable (x) with the same name (x) in side {...} it does not create any new variable but actually override the previously declared variable.

answered Apr 25, 2018 at 15:34

Mamun

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