node complains variable is undefined in conditional assignment?

Question

I'm trying to let a user optionally pass in an options parameter to a function to override a default variable like this:

 let methodName = (options && options.methodName) || 'getSpaces';

However, when I put this line into my node CLI I get an error: ReferenceError: options is not defined.

How come I can't do this sort of thing?

Check on how undefined works: https://stackoverflow.com/questions/3390396/how-to-check-for-undefined-in-javascript — Chris Cousins, Aug 30 '18 at 17:58
So, where *did* you define `options`? Show that part of the code as well. — Bergi, Aug 30 '18 at 18:03
@Bergi That is exactly the problem, he doesn't, I assume he runs this code directly in the node terminal. — Християн Христов, Aug 30 '18 at 18:33
@ХристиянХристов He's talking about a function with a parameter and a user of that function, doesn't look like he's running it in the REPL. — Bergi, Aug 30 '18 at 19:07

score 2 · Accepted Answer · answered Aug 30 '18 at 18:05

2

If you don't know whether options will be even defined or not, you can do:

let methodName = (typeof(options) !== 'undefined' && options.methodName) || 'getSpaces';

answered Aug 30 '18 at 18:05

JCOC611

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score 1 · Answer 2 · answered Aug 30 '18 at 18:05

Do it like this

let options;
let methodName = (options && options.methodName) || 'getSpaces';

You are trying to access variable that does not exist, that is the reason it throws this error. You will have the same error if you paste the same code even in the browser console, because the same reasons.

score 0 · Answer 3 · answered Aug 30 '18 at 18:08

The function declaration seems wrong to me. It can be either one of the below:

    let methodName = (options) => ((options && options.methodName)  || 'getSpaces');
    let otherMethod = (methodName = "getSpaces") => (methodName)
    console.log(methodName())  //getSpaces
    console.log(methodName({methodName:"testMethod"}))  //testMethod
    console.log(otherMethod())  //getSpaces
    console.log(otherMethod("anotherTestMethod"))  //anotherTestMethod

node complains variable is undefined in conditional assignment?

3 Answers3