How to parse string into function property in javascript

Question

I created custom stringify method to stringify function as follow

var myStringify=function (obj) {
      return JSON.stringify(obj, function (key, value) {
        if (value instanceof Function || typeof value == 'function') {
          return value.toString();
        }
        return value;
      });
    }

But when I have no idea about parsing string function into function object. Here is my example

var parsed=JSON.parse(jsonString);

After processing JSON.parse function, I got following

parsed.run field has string of function

console.log(parsed.run)  // output is "function(){console.log('foo');}"

I want this function string back into property of parsed object,

{run:"function(){console.log('foo');}"}

into

{run:function(){console.log('foo');}}

how should I do?

@RayonDabre, I know your point. I posted for short note: complete is parsed={run:"function(){console.log('foo');}"}. Thanks — KyawLay
– KyawLay, Commented Mar 10, 2016 at 11:08
Tell me why would this situation arise ? What you want to achieve ? — Rayon
– Rayon, Commented Mar 10, 2016 at 11:09
I want to pass some object to webworker and want to run object function inside webworker. if I can convert function string back to function I can run object function from webworker. — KyawLay
– KyawLay, Commented Mar 10, 2016 at 11:13

Thomas · Accepted Answer · 2016-03-10 11:59:56Z

1

a regex to match function-strings:

var parseFunctionString = /^\s*function(\s+[a-z0-9$_]*)?\(([^)]*)\)\s*\{([\s\S]*)\}\s*$/i;
//extended regExp, to handle fat-arrow-notation
//var parseFunctionString = /^\s*(?:function(\s+[a-z0-9$_]*)?\(([^)]*)\)\s*\{([\s\S]*)\}|\(([^)]*)\)\s*=>([\s\S]*)|([a-z0-9$_]+)\s*=>([\s\S]*))\s*$/i;

and the usage:

JSON.parse(input, function(k,v){
    var m = typeof v === "string" && v.match(parseFunctionString);
    if(m){
        return Function(m[2], m[3]);
        //if you include the extended regExp
        //return Function(m[2] || m[4] || m[6], m[3] || "return "+( m[5] || m[7] ));

        //return Function("return " + m[0])();
    }
    return v;
})

answered Mar 10, 2016 at 11:59

Thomas

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Comments

gurvinder372 · Accepted Answer · 2016-03-10 11:22:08Z

1

Get the body first

var string = parsed.run;
var body = string.substring(string.indexOf("{") + 1, string .lastIndexOf("}"));

Now create a new function object and execute

new Function(body)();

You can try a simple demo on your browser console as

var string = "function(){console.log('foo');}";
var body = string.substring(string.indexOf("{") + 1, string .lastIndexOf("}"));
new Function(body)(); //outputs foo

Refactor this into a function

function convertBodyToFunction(body)
{
   body = string.substring(string.indexOf("{") + 1, string .lastIndexOf("}"));
   return new Function(body);
}
convertBodyToFunction(parsed.run)();

edited Mar 10, 2016 at 11:22

answered Mar 10, 2016 at 11:15

gurvinder372

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