With the following code JsLint warns that y is already defined in the 2nd block. I do this fairly often and don't think it is a syntax error since the variable is defined in a different block.

Should I really be using different variable names even though it is in a different block? Is the scope defined by the code block of the if statement or only scoped for a function block?

function x() {
  if (condition1) {
    var y = 0;
    // use y
  }
  if (condition2) {
    var y = 20;
    // use y
  }
}

With the following code JsLint warns that y is already defined in the 2nd block. I do this fairly often and don't think it is a syntax error since the variable is defined in a different block.

Should I really be using different variable names even though it is in a different block? Is the scope defined by the code block of the if statement or only scoped for a function block?

function x() {
  if (condition1) {
    var y = 0;
    // use y
  }
  if (condition2) {
    var y = 20;
    // use y
  }
}

• javascript
• jslint

Share Improve this question Follow asked Oct 16, 2013 at 17:43 BrennanBrennan 11.7k1616 gold badges6868 silver badges8686 bronze badges 1

• I would not suggest using var at all. This will only expose y to everything else of the if scope that you have defined, which could be harmful given where and what y means to the function/global scope. Use let instead. - stackoverflow./a/11444416/3670089 – Yashash Gaurav Commented May 26, 2020 at 16:19

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3 Answers 3

Sorted by: Reset to default 8

Declare it once

function x() {
    var y;
    if (condition1) {
        y = 0;
    }
    if (condition2) {
        y = 20;
    }
}

JS will have block scoping in the future, but it's not widely implemented yet.

There is no different scope inside if, for and while statements, but there is in functions.

I know there is accepted answer to this already, but I think what you are looking for is a let statement.

Please refer to this answer to understand variable scoping (let vs var): https://stackoverflow./a/11444416/3670089