Javascript shorthand way to assign true/false to variable if a array element exists

Question

I was hoping I could just assign true / false to a variable if my element exists in an associative array.

I tried this --

var finalDisExist = stepsArray['stepIDFinal'];

-- of course this does exactly what you would think it does (assigning the object to the variable.

But I am pretty sure I have seen something close to this before, can someone tell me what I am missing?

Thanks! Todd

score 6 · Accepted Answer · answered Apr 16 '12 at 18:36

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Perhaps, the quickest and best way is stepsArray.hasOwnProperty('stepIDFinal').

NB: Do NOT use 'stepIDFinal' in stepsArray, since this will check the entire prototype chain for your "hashmap" object and detect toString among others...

answered Apr 16 '12 at 18:36

Alexander Pavlov

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...scratch that, you're right. I was thinking of... not sure what. Although checking `'stepIDFinal' in stepsArray` wouldn't be an issue since there's no native `stepIDFinal` property on `Object.prototype`. – Apr 16 '12 at 18:54
@amnotiam: right, yet I believe it's not the only key OP might want to use :) And we've hit this "toString"-ish issue a few times while using the `in` operator. – Alexander Pavlov Apr 17 '12 at 08:02

Tomasz Nurkiewicz · Answer 2 · 2012-04-16T18:54:54.627

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Maybe this?

var finalDisExist = !!stepsArray['stepIDFinal'];

The first negation takes everything that was falsy (like undefined and 0) into true and the second one to real false - and vice versa. This means if stepsArray['stepIDFinal'] is equal to null or 0, finalDisExist will be false...

edited Apr 16 '12 at 18:54

answered Apr 16 '12 at 18:35

Tomasz Nurkiewicz

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score 2 · Answer 3 · answered Apr 16 '12 at 18:36

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You'll want to use stepsArray.hasOwnProperty("stepIDFinal") if I'm not mistaken.

answered Apr 16 '12 at 18:36

Hacknightly

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score 1 · Answer 4 · answered Apr 16 '12 at 18:35

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Do you mean

var finalDisExist = !!stepsArray['stepIDFinal'];

or maybe

var finalDisExist = "undefined" !== typeof stepsArray['stepIDFinal'];

?

answered Apr 16 '12 at 18:35

Thomas

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Javascript shorthand way to assign true/false to variable if a array element exists

4 Answers4