let variable is not defined

Question

function formatToStandardizedDate(from, to){

    const from_date = moment(from);

    if(to){
        let to_date = moment(to);
    }else{
        let to_date = null;
    }
}

console.log(formatToStandardizedDate("2017-04-19 00:00:00",null))

What's wrong with my code above? if to is null it at least assign a null to to_date but I got error of to_date of undefined error. Why?

Possible duplicate of [What's the difference between using "let" and "var" to declare a variable?](http://stackoverflow.com/questions/762011/whats-the-difference-between-using-let-and-var-to-declare-a-variable) — mxr7350, Apr 12 '17 at 11:43
You'd need to define the `let` outside of the block if you want to use it outside the block. — Dave Newton, Apr 12 '17 at 11:44

Jai · Answer 1 · 2017-04-12T12:05:24.343

6

You can't use same variable names with let keyword. It will throw errors if you try to do this.

Instead you have to use ternary operator:

let to_date = to ? moment(to) : null;

or declare it once above in the function and update the variable

function formatToStandardizedDate(from, to){
    const from_date = moment(from);
    let to_date = null; // initialize the variable with null
    if(to)
      to_date = moment(to); // <---here update the variable with new value.
}

_{Updated as per JaredSmith's comment and that seems good.}

edited Apr 12 '17 at 12:05

answered Apr 12 '17 at 11:43

Jai

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But then it might as well be a `const`. – Dave Newton Apr 12 '17 at 11:44
but i guess constants can't be updated to new values. – Jai Apr 12 '17 at 11:47
2

Note that the else clause is totally unnecessary, you could just initialize `let to_date = null;` and only change it if the second parameter is truthy `if (to) to_date = moment(to);`. I still prefer your ternary example in any case. – Jared Smith Apr 12 '17 at 12:01
@JaredSmith totally agree with you. – Jai Apr 12 '17 at 12:03

let variable is not defined

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