JSON.parse with functions inside

Question

I have a string that if I turn it into OBJ it works correctly.

var obj = JSON.parse('{ "placeholder": "Hello...."} ');

then I put it in the tagEditor plugin in this way $('textarea').tagEditor(obj);

But I also need to evaluate within if there is a function and that it works, in this way.

var obj = JSON.parse('{ "placeholder": "Hello....", "onChange":"function(a,b,c)}{ }"} ');

and I put it....... $('textarea').tagEditor(obj);

but when I do that I get error Uncaught SyntaxError: Unexpected string in JSON at position 38

Actually I want to evaluate the function that is by string, As you can see when I put the event "onchange" and the function within the object this has to evaluate it for the plugin to work Does anyone know how to solve that problem?

See the snippet - your new edited code looks to work fine (or, at least, does not throw a SyntaxError) — CertainPerformance
– CertainPerformance, Commented Jun 29, 2019 at 20:37
tagEditor does not evaluate the object if I put that event, apparently it is an error in the parse, or I do not know =/ — LΞИIИ
– LΞИIИ, Commented Jun 29, 2019 at 20:41

CertainPerformance · Accepted Answer · 2019-06-29 20:32:14Z

You should first declare the function, then call toString on the function (which will automatically escape the 's, which is the problem in your current syntax):

function x(a, b, c){
  return '';
}
const stringified = JSON.stringify({
  placeholder: "Hello....",
  onChange: x.toString()
});

Specifically, because the string delimiters for the function property value use ', you need to escape the 's used inside. (turn

"onChange":"function(a,b,c)}{ return ''; }"

into

"onChange":"function(a,b,c)}{ return \'\'; }"

)

But I wouldn't recommend doing that manually, it'll be pretty tedious and somewhat error-prone - the toString() method is probably a better option.

Thanks for answering, I just updated the question, I really need the function to be evaluated

Randy Casburn · Accepted Answer · 2019-06-29 20:45:27Z

1

The syntax is invalid:

var obj = JSON.parse('{ "placeholder": "Hello....", "onChange":"function(a,b,c)}{ return ''; }"} ');

You JSON is quoted properly, but you preempted the single quotes inside the function declaration. So change it to escaped quotes:

EDIT: to then evaluate the function you must use eval() like this. I have no idea what your intent is for the onChange handler so I modified it so it would actually work:

var obj = JSON.parse('{ "placeholder": "Hello....", "onChange":"function handler(e){ console.log(e.target.value); }"} ');
console.log(obj);
eval(obj.onChange);
document.querySelector('input').onchange = handler;

<input>
<div></div>

edited Jun 29, 2019 at 20:45

answered Jun 29, 2019 at 20:32

Randy Casburn

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2 Comments

Bergi Over a year ago

Hm, this doesn't seem to fit the "Unexpected string in JSON" error message though. But your example works, so it must be something else anyway.

LΞИIИ Over a year ago

Thanks for answering, I just updated the question, I really need the function to be evaluated

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