字符串化JSON内部对象的最佳实践

Question

Basically I have something like this:

MyClass

var MyClass = function() {
  this.num = 123;
  this.obj = new MyInnerClass();
};

MyClass.prototype.stringify = function() {
  return JSON.stringify(this);
};

MyInnerClass

var MyInnerClass = function() {
  this.foo = 456;
  this.bar = 'bonjour!';
};

MyInnerClass.prototype.stringify = function() {
  return JSON.stringify(this, function(k, v) {
    // ignores 'foo' attribute
    return k !== 'foo' ? v : undefined;
  });
};

Each class has its own stringify implementation, so when I do:

var mc = new MyClass();
mc.stringify();

I would like something like calling MyClass.stringify should stringify my mc object, but respecting inner objects stringify implementations. Once we don't have control over the JSON.stringify method logic, is there a good way to do that?

Thank you!

Answer 1

If you look on MDN at JSON.stringify , you'll see a section that talks about a toJSON property

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.

Basically, define a toJSON method for your Object which creates another Object , but one that can be serialised as you desire. Then JSON.stringify will serialise the return of your toJSON function instead, ie

var MyClass = function() {
  this.num = 123;
  this.obj = new MyInnerClass();
};

var MyInnerClass = function() {
  this.foo = 456;
  this.bar = 'bonjour!';
};

MyInnerClass.prototype.toJSON = function () {
    // shallow clone `this`, except .foo
    var o = Object.create(null), k, blacklist = ['foo'];
    for (k in this) // loop over enumerable properties
        if (Object.prototype.hasOwnProperty.call(this, k)) // ignore inherited properties
            if (blacklist.indexOf(k) === -1) // ignore blacklisted properties
                o[k] = this[k]; // add to our clone
    return o;
};

JSON.stringify(new MyClass()); // '{"num":123,"obj":{"bar":"bonjour!"}}'

This will also replace your need for the current stringify method.

---

Sadly you can't call JSON.stringify(this) inside .toJSON because it becomes circular and you get RangeError: Maximum call stack size exceeded , but you'd not get the desired result this way anyway as it would be serialised a second time, giving you a String in your JSON .