Reverse of JSON.stringify?

I'm stringyfing an object like {'foo': 'bar'}

How can I turn the string back to an object?

你需要JSON.parse()这个字符串。

var str = '{"hello":"world"}';
try {
  var obj = JSON.parse(str); // this is how you parse a string into JSON 
  document.body.innerHTML += obj.hello;
} catch (ex) {
  console.error(ex);
}

JSON.parse与JSON.stringify相反。

JSON.stringify and JSON.parse are almost oposites, and "usually" this kind of thing will work:

var obj = ...;
var json = JSON.stringify(obj);  
var obj2 = JSON.parse(json);

so that obj and obj2 are "the same".

However there are some limitations to be aware of. Often these issues dont matter as you're dealing with simple objects. But I'll illustrate some of them here, using this helper function:

function jsonrepack( obj ) { return JSON.parse(JSON.stringify(obj) ); }

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

var o = new MyClass();
var oo = jsonrepack(o);
console.log(oo.bar); // undefined
console.log( oo instanceof MyClass ); // false

var o = {};
var oo = jsonrepack(o);
console.log( o === oo ); // false

jsonrepack( { f:function(){} } ); // Returns {}

jsonrepack(new Date(1990,2,1)); // Returns '1990-02-01T16:00:00.000Z'

var v = { x:undefined }
console.log("x" in v);              // true
console.log("x" in jsonrepack(v));  // false

x = { f:"foo", toJSON:function(){ return "EGAD"; } }
jsonrepack(x) // Returns 'EGAD'

I'm sure there are issues with other built-in-types too. (All this was tested using node.js so you may get slightly different behaviour depending on your environment too).

When it does matter it can sometimes be overcome using the additional parameters of JSON.parse and JSON.stringify . For example:

function MyClass (v) {
   this.date = new Date(v.year,1,1);
   this.name = "an object";
};

MyClass.prototype.dance = function() {console.log("I'm dancing"); }

var o = new MyClass({year:2010});
var s = JSON.stringify(o);

// Smart unpack function
var o2 = JSON.parse( s, function(k,v){
  if(k==="") { 
     var rv = new MyClass(1990,0,0);
     rv.date = v.date;
     rv.name = v.name;
     return rv
  } else if(k==="date") {
    return new Date( Date.parse(v) );
  } else { return v; } } );

console.log(o);             // { date: <Mon Feb 01 2010 ...>, name: 'an object' }
console.log(o.constructor); // [Function: MyClass]
o.dance();                  // I'm dancing

console.log(o2);            // { date: <Mon Feb 01 2010 ...>, name: 'an object' }
console.log(o2.constructor) // [Function: MyClass]        
o2.dance();                 // I'm dancing

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