Unexpected token : at window.onload

Question

I'm a beginner in Javascript and I have a little problem with the eval() function. So, first I get some data through an API :

const xhr = new XMLHttpRequest();
xhr.open('GET', url, false);
xhr.send(null);

So, at that point, I know that xhr.response is for example :

"{"data":[{"id":41462,"created_at":"2017-11-13 [...]}"

Now, I want to make a dictionary with it, so I do :

var req = eval(xhr.response);

But the console shows me "Uncaught SyntaxError: Unexpected token : at window.onload" at the eval() step. And I don't know really why... any tips ?

that looks like JSON instead of doing eval do JSON.parse(xhr.response) it will work — sumeet kumar
– sumeet kumar, Commented Nov 13, 2017 at 17:02

Quentin · Accepted Answer · 2017-11-13 17:04:08Z

2

eval expects to be passed a chunk of JavaScript. A JSON representation of an object is not (by itself) valid JavaScript.

To parse JSON, use JSON.parse and not eval.

answered Nov 13, 2017 at 17:04

community wiki

Quentin

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5 Comments

evolutionxbox Over a year ago

Surely any valid JSON will also be parsed as valid JS? Not trying to be contrarian, but do you have an example of valid JSON, but not valid JS?

user47589 Over a year ago

@evolutionxbox not always. stackoverflow.com/questions/23752156/…

evolutionxbox Over a year ago

@Amy good to know. A̶l̶t̶h̶o̶u̶g̶h̶ ̶I̶ ̶d̶o̶n̶'̶t̶ ̶t̶h̶i̶n̶k̶ ̶i̶t̶ ̶s̶a̶t̶i̶s̶f̶i̶e̶s̶ ̶O̶P̶'̶s̶ ̶e̶r̶r̶o̶r̶.̶ Nevermind... it does.

Arthur R. Over a year ago

Thank's a lot! I didn't know about JSON, you're helpful :)

evolutionxbox Over a year ago

@Quentin ooooo. Interesting

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