converting a function object to string | "function(){...}"

Question

func=function() {foo=true}
alert(JSON.stringify(func));

alerts "undefined"

obj={foo: true}
alert (JSON.stringify(obj));

alerts: "{foo: true}"

Why is this? As far as I understand JSON.stringify() converts an object to a json string, but I notice this doenst work for a "function object".

Btw searching for "function object" is hell in search engine land, because the only results I get out of google are about how objects are functions and functions are objects, but little about an actual function object.

"The Function constructor creates a new Function object. In JavaScript every function is actually a Function object." https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function

"Ok google: so every javascript function is an object, and every object is an function..." its the same, but it acts differenlty? I dont get it. So I am turning to stackoverflow. Can anyone enlighten me and explain why JSON.stringify(function() {foo=true}) does not work?

(ps. my goal is to turn function() {foo=true} into "function() {foo=true}" I am not looking for a workaround. I want to know why it doenst work to convert the function object to (json) string.

Andreas Louv · Accepted Answer · 2014-03-05 11:10:06Z

3

You can use Function.prototype.toString()

var a = function() { return 1; };

console.log( a.toString() ); // "function() { return 1; }"

Im not sure about the support though.

answered Mar 5, 2014 at 11:10

Andreas Louv

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3 Comments

RobG Over a year ago

It's been around since at least ed 1 so should be fine.

058WistWol Over a year ago

Thanks for that example. I wasnt aware toString() could work :)

Andreas Louv Over a year ago

@058WistWol Note that you cannot use .toString() on native functions like alert, console.log, etc: alert.toString() -> function alert() { [native code] }"

kcak11 · Accepted Answer · 2014-03-05 11:09:57Z

1

Reason: JSON --> JavaScript Object Notation. JSON is a mechanism to persist (serialize) the state of a JavaScript object in a String so that it can be reused later / sent to server / process in other way.

function is not an object --> so its state cannot be serialized.

The return value of a function can however be serialized in case the return is a non-function value.

answered Mar 5, 2014 at 11:09

kcak11

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5 Comments

RobG Over a year ago

"function is not an object". Yes it is, however there is no serialisation for functions in the JSON grammar.

kcak11 Over a year ago

@RobG think in terms of any programming language, a function is associated with the behavior it does and not the characteristics it holds. So calling function an object is wrong.

058WistWol Over a year ago

"The Function constructor creates a new Function object. In JavaScript every function is actually a Function object." developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… (they write "function" in sub, but still its really confusing.. is there a special function object and are functions==objects or are functions===objects or perhaps still function!==object) it doenst really mather. But still huh

Chris Over a year ago

A Function is an Object is JavaScript, so this answer is not as clear as it could be. To see this in action try: var x = function() { return 42; };, x instanceof Function // true, x instanceof Object // true. The correct answer has been mentioned by @RobG, that is the JSON specification does not describe how to serialise Functions.

nnnnnn Over a year ago

"think in terms of any programming language" - You can't just assume all programming languages will work the same way. Some programming languages don't have functions. Some don't have objects. In JS a function is definitely an object.

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