Javascript - If Statement Returning Null Despite Condition

Question

I'm trying to figure out why my if statement is sending true output's despite accounting for null situations in my if statement. Can someone explain what is wrong with my conditions and the reason why null triggers for true?

if(startDate || startDate != null){
            filterQuery.push('dateStart=' + startDate);
}

outputs dateStart=null in instances where there is a null value.

If `startDate` is really `null`, that condition will definitely be false. (It will also be false if `startDate` is `undefined`.) — T.J. Crowder, Feb 19 '17 at 19:12
There's no need for the first part of that condition, though. — T.J. Crowder, Feb 19 '17 at 19:13
Don't tell me it is the string `"null"`, that would be really funny. Whoever thinks assigning the string `"null"` to a variable is a good idea, is asking for getting confused. — trincot, Feb 19 '17 at 19:14
`null` should be `"object"` type, you `startDate` is actually `"null"`, not `null`, hence condition 1 is true. — Eduardo Escobar, Feb 19 '17 at 19:15
`startDate` appears to be `"null"`. Can you show us how you defined this value? Please, [edit] your question and provide a [Minimal, Complete, and Verifiable example](http://stackoverflow.com/help/mcve). — Sebastian Simon, Feb 19 '17 at 19:15

score 2 · Accepted Answer · edited May 23 '17 at 10:29

2

You've said that typeof startDate gives you "string". That's your problem: "null" is a truthy value (so it passes the first test) that is != null (so it passes the second test). So your condition is true and the output concatenate the string "null" to your error message.

edited May 23 '17 at 10:29

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answered Feb 19 '17 at 19:14

T.J. Crowder

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Great call. I should have defaulted to using `typeof` before jumping to the assumption that it was an actual `null` value – cphill Feb 19 '17 at 19:15

Javascript - If Statement Returning Null Despite Condition

1 Answers1