Check for array in JS

Question

I'm trying to check a value in JS that on page load is returned as a single-element array and after an ajax function returns as a string. I don't know why it's doing this but I'm trying to role with it.

So, using console.log(value) I get array ['Scranton'] on page load, and the ajax even returns string "Scranton"

When trying to check this variable, this does not work as I intended:

if ( value === 'Scranton' || value === ['Scranton']){
    ...
}

Any help is appreciated!

Two different arrays with the same content are never equal: [] === [] is false. See stackoverflow.com/q/7837456/218196 for general solutions. — Felix Kling
– Felix Kling, Commented Aug 14, 2014 at 13:47

Richard Dalton · Accepted Answer · 2014-08-14 13:48:16Z

3

This would probably work but I would try and fix the underlying issue instead of working around it.

if ( value === 'Scranton' || value[0] === 'Scranton'){
    ...
}

answered Aug 14, 2014 at 13:48

Richard Dalton

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2 Comments

psorensen Over a year ago

for the record, this also worked. My choice of answer was merely a matter of preference. Thanks!

Richard Dalton Over a year ago

@PeteSorensen np, I upvoted the other answer I thought it was good.

Pablo Mescher · Accepted Answer · 2014-08-14 13:57:24Z

2

You can use indexOf for both an array and a string, so value.indexOf("Scranton") !== -1 will work (just tested this on the console).

However you must first check for null/false/undefined or it will error.

if (value && value.indexOf("Scranton") !== -1) {}

EDIT: As Felix said, this will also be true for any string containing "Scranton". If this is a problem, then you can check for indexOf == 0 instead, which will be true for any string starting with "Scranton". It really depends on your concrete problem if this solution fits you. Use with care.

edited Aug 14, 2014 at 13:57

answered Aug 14, 2014 at 13:48

Pablo Mescher

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2 Comments

Felix Kling Over a year ago

That will be true for "fooScrantonbar" as well though.

Pablo Mescher Over a year ago

You are right, perhaps he should check for 0 instead. I'll update my answer.

riovel · Accepted Answer · 2014-08-14 15:34:35Z

1

if (Object.prototype.toString.call(value) === '[object Array]') {
    if (value.indexOf('Scranton') != -1) {
        /*  */
    }
} else {
    if (value === 'Scranton') {
        /*  */
    }
}

Edit 1:

First, you need to check if "value" is an array. If it's an array and contains the string "Scranton", you can find it using value.indexOf(). And if "value" is not an array, you can directly compare it with the string 'Scranton'.

edited Aug 14, 2014 at 15:34

answered Aug 14, 2014 at 14:02

riovel

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1 Comment

MightyPork Over a year ago

Please, add some explanation to your answer. As it is now, it's been flagged as "low quality".

danemacmillan · Accepted Answer · 2014-08-14 14:01:27Z

What does "after an ajax function" mean? The page loads with a default variable that has been assigned an array value, and then an Ajax request is made, which changes this default variable, and instead of an array being assigned, it assigns a string? Assuming this "ajax function" changes the default variable to the response text from the server, there is your problem: Ajax--like any other request--is text-based, so it is a string. If you are responding to the Ajax request with a JSON string, built on the server, it needs to be parsed in the browser, so it can be reinterpreted as an array. See the JSON.parse method.

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