How to tell JavaScript that my variable is an array and not a string?

Question

I'm using flask and my backend returns to AJAX a response in the form of a python list, and then JavaScript understands it as a string, but that's a problem because I have to iterate over that list.

All i could find on the internet is how to check the type of a variable, but couldn't find any method (which in python is pretty straightforward) to change it

Array.isArray() to check for array..typeof keyword to know the type of variable — AConsumer
– AConsumer, Commented Aug 29, 2019 at 2:42
But the variable is a string @ShivendraGupta - so Array.isArray and typeof return false and "string" respectively. — Jack Bashford
– Jack Bashford, Commented Aug 29, 2019 at 2:44
Most of the times HTTP response are coming like a string. So you can do two things. First, you have to check it is that data are string type? if so convert them into an object. typeof response === 'string' then JSON.parse( response ) — Dananjaya Ariyasena
– Dananjaya Ariyasena, Commented Aug 29, 2019 at 2:45

Asif Islam · Accepted Answer · 2019-08-29 03:01:00Z

0

The Array.isArray() method determines whether the passed value is an Array or not.

var someNumbers = [1,2,3];
console.log( Array.isArray( someNumbers ) );

and if it is an array it will return

true

Check this link to know more about Array.isArray

answered Aug 29, 2019 at 3:01

Asif Islam

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1 Comment

David Thomas Over a year ago

That's not the question that's being asked; OP knows that JavaScript is working with a string, but s/he wants to force his JavaScript to understand it's really an array.

NoobTW · Accepted Answer · 2019-08-30 08:34:21Z

0

If your response is a string, you can use JSON.parse to turn it into an JS Object/Array.

var response = someAjaxStuff(...);
// response is a string
response = JSON.parse(response);
// now reponse is an Object/Array

If you use AJAX with jQuery, you can also use dataType:

$.ajax({
    url: 'https://example.com/api/somejson',
    dataType: 'json',
    method: 'get',
    success: function(res) {
        // console.log res will be an object/array here.
    }

});

But if you're writing your own API, I suggest you have to add the right header to tell browser that it is a JSON format instead of string.

For flask you can use jsonify (reference):

return jsonify(somedict)

edited Aug 30, 2019 at 8:34

answered Aug 29, 2019 at 2:45

NoobTW

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4 Comments

David Spira Over a year ago

i'm trying the first option you presented, and i get the console error: "Uncaught SyntaxError: Unexpected token u in JSON at position 2"

NoobTW Over a year ago

Maybe your string is not a valid JSON. You can validate your string here.

David Spira Over a year ago

my string is actually a python list [[a,b,c],[d,e,f],...]

NoobTW Over a year ago

If that's not a JSON, it's impossible for JS to read that string (unless you write a parser for that). Make sure your API can response a valid JSON.

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