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 is entirely possible to create functions from string without eval()

var obj = {a:function(a,b){
    return a+b;
}};

var serialized = JSON.stringify(obj, function(k,v){
    //special treatment for function types
    if(typeof v === "function")
        return v.toString();//we save the function as string
    return v;
});
/*output:
"{"a":"function (a,b){\n        return a+b;\n    }"}"
*/

now some magic to turn string into function with this function

var compileFunction = function(str){
    //find parameters
    var pstart = str.indexOf('('), pend = str.indexOf(')');
    var params = str.substring(pstart+1, pend);
    params = params.trim();

    //find function body
    var bstart = str.indexOf('{'), bend = str.lastIndexOf('}');
    var str = str.substring(bstart+1, bend);

    return Function(params, str);
}

now use JSON.parse with reviver

var revivedObj = JSON.parse(serialized, function(k,v){
    // there is probably a better way to determ if a value is a function string
    if(typeof v === "string" && v.indexOf("function") !== -1)
        return compileFunction(v);
    return v;
});

//output:

 revivedObj.a

 function anonymous(a,b
 /**/) {

    return a+b;

 }

 revivedObj.a(1,2)
3

Answer 2

To my knowledge, there are no serialization libraries that persist functions - in any language. Serialization is what one does to preserve data. Compilation is what one does to preserve functions.

Answer 3

I've had a similar requirement lately. To be clear, the output looks like JSON but in fact is just javascript.

JSON.stringify works well in most cases, but "fails" with functions.

I got it working with a few tricks:

1. make use of replacer (2nd parameter of JSON.stringify())
2. use func.toString() to get the JS code for a function
3. remember which functions have been stringified and replace them directly in the result

And here's how it looks like:

// our source data
const source = {
    "aaa": 123,
    "bbb": function (c) {
        // do something
        return c + 1;
    }
};

// keep a list of serialized functions
const functions = [];

// json replacer - returns a placeholder for functions
const jsonReplacer = function (key, val) {
    if (typeof val === 'function') {
  	    functions.push(val.toString());
        
        return "{func_" + (functions.length - 1) + "}";
    }
        
    return val;
};

// regex replacer - replaces placeholders with functions
const funcReplacer = function (match, id) {
   return functions[id];
};

const result = JSON
    .stringify(source, jsonReplacer)               // generate json with placeholders
    .replace(/"\{func_(\d+)\}"/g, funcReplacer);   // replace placeholders with functions

// show the result
document.body.innerText = result;

body { white-space: pre-wrap; font-family: monospace; }

Important: Be careful about the placeholder format - make sure it's not too generic. If you change it, also change the regex as applicable.