Is there any possibility to have JSON.stringify preserve functions?

Question

Take this object:

x = {
 \"key1\": \"xxx\",
 \"key2\": function(){return this.key1}
}

If I do this:

y = JSON.parse( JSON.st         


        

Answer 1

It seems that people landing here are dealing with structures that would be valid JSON if not for the fact that they contain functions. So how do we handle stringifying these structures?

I ran into the problem while writing a script to modify RequireJS configurations. This is how I did it. First, there's a bit of code earlier that makes sure that the placeholder used internally (">>>F<<<") does not show up as a value in the RequireJS configuration. Very unlikely to happen but better safe than sorry. The input configuration is read as a JavaScript Object, which may contain arrays, atomic values, other Objects and functions. It would be straightforwardly stringifiable as JSON if functions were not present. This configuration is the config object in the code that follows:

// Holds functions we encounter.
var functions = [];
var placeholder = ">>>F<<<";

// This handler just records a function object in `functions` and returns the 
// placeholder as the value to insert into the JSON structure.
function handler(key, value) {
    if (value instanceof Function) {
        functions.push(value);
        return placeholder;
    }

    return value;
}

// We stringify, using our custom handler.    
var pre = JSON.stringify(config, handler, 4);

// Then we replace the placeholders in order they were encountered, with
// the functions we've recorded.
var post = pre.replace(new RegExp('"' + placeholder + '"', 'g'),
                       functions.shift.bind(functions));

The post variable contains the final value. This code relies on the fact that the order in which handler is called is the same as the order of the various pieces of data in the final JSON. I've checked the ECMAScript 5th edition, which defines the stringification algorithm and cannot find a case where there would be an ordering problem. If this algorithm were to change in a future edition the fix would be to use unique placholders for function and use these to refer back to the functions which would be stored in an associative array mapping unique placeholders to functions.

Answer 2

I ran into the same problem, There was another post similar to yours found json-stringify-function. the following may be useful to you:

var JSONfn;
if (!JSONfn) {
    JSONfn = {};
}

(function () {
  JSONfn.stringify = function(obj) {
    return JSON.stringify(obj,function(key, value){
            return (typeof value === 'function' ) ? value.toString() : value;
        });
  }

  JSONfn.parse = function(str) {
    return JSON.parse(str,function(key, value){
        if(typeof value != 'string') return value;
        return ( value.substring(0,8) == 'function') ? eval('('+value+')') : value;
    });
  }
}());

Code Snippet taken from Vadim Kiryukhin's JSONfn.js or see documentation at Home Page

Answer 3

The naughty but effective way would be to simply:

Function.prototype.toJSON = function() { return this.toString(); }

Though your real problem (aside from modifying the prototype of Function) would be deserialization without the use of eval.

Answer 4

Technically this is not JSON, I can also hardly imagine why would you want to do this, but try the following hack:

x.key2 = x.key2.toString();
JSON.stringify(x)  //"{"key1":"xxx","key2":"function (){return this.key1}"}"

Of course the first line can be automated by iterating recursively over the object. Reverse operation is harder - function is only a string, eval will work, but you have to guess whether a given key contains a stringified function code or not.

Answer 5

You can't pack functions since the data they close over is not visible to any serializer. Even Mozilla's uneval cannot pack closures properly.

Your best bet, is to use a reviver and a replacer.

https://yuilibrary.com/yui/docs/json/json-freeze-thaw.html

The reviver function passed to JSON.parse is applied to all key:value pairs in the raw parsed object from the deepest keys to the highest level. In our case, this means that the name and discovered properties will be passed through the reviver, and then the object containing those keys will be passed through.

Answer 6

This is what I did https://gist.github.com/Lepozepo/3275d686bc56e4fb5d11d27ef330a8ed

function stringifyWithFunctions(object) {
  return JSON.stringify(object, (key, val) => {
    if (typeof val === 'function') {
      return `(${val})`; // make it a string, surround it by parenthesis to ensure we can revive it as an anonymous function
    }
    return val;
  });
};

function parseWithFunctions(obj) {
  return JSON.parse(obj, (k, v) => {
    if (typeof v === 'string' && v.indexOf('function') >= 0) {
      return eval(v);
    }
    return v;
  });
};