Object.create, not correct when JSON.stringify the object

Question

I have tried to creates a new object b from object a using Object.create

var a ={}; 
var b = Object.create( a );

a.n = 1;
b.m = 2;

When I iterate two object through for .. in .. its showing correct values . but JSON.stringify not printing correct string .

JSON.stringify( b )

It supposed to print like {"n":1,"m":2} . but it print like {"m":2} only . Any suggestions why?

I have added it in jsfiddle . link of jsfiddle http://jsfiddle.net/V3Nxs/

jsfiddle is blocked here. And including the complete question makes things easier for everyone. — Thilo, May 16 '13 at 11:55
@rab: No, put the relevant information **in the question**. Or don't you want to make it easy for people to help you? — T.J. Crowder, May 16 '13 at 11:55

score 4 · Answer 1 · answered May 16 '13 at 11:57

4

This is becasue n is the prototype property of b and JSON.stringify only works for those properties which returns true for hasOwnProperty on the object.

answered May 16 '13 at 11:57

Ankur

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Specifically: `JSON.stringify` only includes *enumerable*, *own* properties, not properties inherited from the prototype, and not non-enumerable properties. – T.J. Crowder May 16 '13 at 11:59
@Ankur Your answer helps with my issue. what is solution for print correct `JSON.stringify` ? – rab May 16 '13 at 12:10

score 1 · Accepted Answer · answered May 16 '13 at 11:57

I updated your fiddle

http://jsfiddle.net/V3Nxs/2/

for( var k in b ){
    if (!b.hasOwnProperty(k)) continue;
    html.push( 'b.'+ k +':' + b[k] );
}

You need to use hasOwnProperty
I changed the index of the second for loop

If you look at what Object.create does, the first argument you pass in is the prototype of the new object. That means that b has everything a has, in the prototype chain. hasOwnProperty fixes this because it only returns true if the property tested is on the object itself, not somewhere up in the prototype chain.

now it behaves as i think you expect.

score 0 · Answer 3 · answered May 16 '13 at 11:57

0

b.n not being defined is expected behavior. To get what you want you might want to try this.

var a = {};
var b = {a:a};

a.n = 1;
b.m = 2;

now b.a.n is set to 1 and JSON.stringify includes it in the output.

answered May 16 '13 at 11:57

jabbink

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Object.create, not correct when JSON.stringify the object

3 Answers3