Fail to `JSON.stringify(this)` when learning OOP (got RangeError: Maximum call stack size exceeded)

Question

function MyClass() {
    this.foo = "foo";
    this.bar = "bar";
}

MyClass.prototype.toJSON = function(space) {
    if (typeof space === 'undefined') space = 4;
    return JSON.stringify(this, null, space);
};

var m = new MyClass();
console.log(m.toJSON());

I ran it in node.js, and got:

MyClass.prototype.toJSON = function(space) {
                                   ^
RangeError: Maximum call stack size exceeded

I don't know why. It makes me confused. Could you please tell me the reason causing this error? And how to fix it?

this in your .toJSON method is a reference to m and stringify will invoke a .toJSON method if it exists on the data it's given. So m.toJSON() calls JSON.stringify(m..., which calls m.toJSON(), which calls JSON.stringify(m..., and so on. — cookie monster
– cookie monster, Commented Aug 16, 2014 at 5:27
That's the answer cookie monster, not just a comment. Here's a comment: You should change if (typeof space === 'undefined') space = 4; to var spc = space ? space : 4;. Then pass spc to JSON.stringify(), as the last argument. — StackSlave
– StackSlave, Commented Aug 16, 2014 at 5:47
Note that reassigning the argument creates potential scope issues. In this case space could assign a global variable. — StackSlave
– StackSlave, Commented Aug 16, 2014 at 5:58
@PHPglue: Don't worry about posting an answer that was already given as a comment. If a person (like me) decides to use a comment to answer the question, that's their (my) problem. ;-) — cookie monster
– cookie monster, Commented Aug 16, 2014 at 16:58

abcdabcd987 · Accepted Answer · 2014-08-16 06:22:11Z

4

I solved this by renaming the .toJSON function to .save.

I found the reason here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify, which says:

If an object being stringified has a property named toJSON whose value is a function, then the toJSON method customizes JSON stringification behavior: instead of the object being serialized, the value returned by the toJSON method when called will be serialized.

So the original code would cause an infinite recursive.

Thanks to @cookie monster and @PHPglue.

Working code:

function MyClass() {
    this.foo = "foo";
    this.bar = "bar";
}

MyClass.prototype.save = function(space) {
    var s = typeof space === 'undefined' ? 0 : 4;
    return JSON.stringify(this, null, s);
};

var m = new MyClass();
console.log(m.save());

answered Aug 16, 2014 at 6:22

abcdabcd987

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1 Comment

Austin Over a year ago

Thank you for this, it helped in 2023 NodeJS project that was reporting a stack size error due to the recursive calling of a class that has a toJSON() function. MacOS and Windows didn't exhibit this behavior, but it was happening on a Linux server.

rnrneverdies · Accepted Answer · 2014-08-16 06:05:55Z

0

@cookie monster really answered the question, maybe this will help though:

function MyClass(){
  this.foo = 'foo';
  this.bar = 'bar';
  this.gotToJSON = false;
}

MyClass.prototype.toJSON = function(space){
  var spc = space ? space : 4;
  if(!this.gotToJSON){
    this.gotToJSON = true;
    var result = JSON.stringify(this, null, spc);
    this.gotToJSON = false;
    return result;
  }
  return;
}

var m = new MyClass;
console.log(m.toJSON());

edited Aug 16, 2014 at 6:05

rnrneverdies

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answered Aug 16, 2014 at 5:55

StackSlave

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Comments

shubham hirap · Accepted Answer · 2023-03-03 04:54:23Z

0

Changing Name

.toJSON

to something else like displayJSON works for me

answered Mar 3, 2023 at 4:54

shubham hirap

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