Question

I have a json string like this:

json = "{'run': 'function() { console.log('running...'); }'}"

How do I run that function inside of the json string?

Answer 1

You’re going to have to use the eval() (doc) function. A lot of people have a lot of feelings about this function. JSON is best for transporting data, not functions (see JSON). The functions ought to lay in the script on the page.
Also there’s a syntax error in your posted code (function is wrapped in single quotes (‘), and so is console.log’s first parameter).
But…

json = "{\"run\":\"function() { console.log('running...'); }\"}"; //Fixed, thanks
obj = JSON.parse(json);
eval(obj.run); //Logs "running..."

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Update:

Oh, and I was mistaken. Eval doesn’t seem to like anonymous functions. With the revised code, it will parse json into an object with a run property that is a String, with value "function() { console.log('running...'); }". But when you eval(obj.run);, you will get a SyntaxError declaring an unexpected (. Presumably, this is the ( in function ().

So, I can think of two ways of dealing with this:

1. Remove the anonymous function in your actual JSON string (so, make your PHP forget about function () {), and eval it. This means it will be called as soon as you eval it.

2. What I think you want, is to be able to evaluate it to an anonymous function, that will be called when you want. So, you could write a wrapper function (you would need to follow option 1 for this as well):

   function returnEval(str) {
       return function () { eval(str); }
   }
   

   This would allow you to call it. So:

   obj = JSON.parse(json);
   obj.run = returnEval(obj.run);
   obj.run(); //Logs "running..."
   

Hope this helps!