How to change object's property value in JSON object

Question

I have the following problem :

var a = {
    'a': '',
    'b': ''
},

b = [1,3],
o = {};

for (i = 0; i<b.length; i++) {
    o['shop' + b[i]] = a;
    o['shop' + b[i]].store = b[i];
}

console.log(JSON.stringify(o));

Expecting shop[n] will be equal to store value, but it's wrong

{
    "shop1" : {
        "a" : "",
        "b" : "",
        "store":3
    },
    "shop3" : {
        "a" : "",
        "b" : "",
        "store":3
    }
}

What's wrong with it?

what do u mean by "store value"

Rajkumar Somasundaram
– Rajkumar Somasundaram

2017-11-29 07:10:16 +00:00
Commented Nov 29, 2017 at 7:10 — Rajkumar Somasundaram
– Rajkumar Somasundaram, Commented Nov 29, 2017 at 7:10

Suraj Rao · Accepted Answer · 2017-11-29 06:57:12Z

2

Because you have a single object to which a refers and when changing it via each iteration you actually change the value for all of them, because you work with the reference which refers to the single object. You can use Object destructing to copy the object for each property in the o.

var a = {
    'a': '',
    'b': ''
};
var b = [1,3];
var o = {};

for (var i = 0; i < b.length; i++) {
    o['shop' + b[i]] = {...a};
    o['shop' + b[i]].store = b[i];
}

console.log(JSON.stringify(o));

edited Nov 29, 2017 at 6:57

Suraj Rao

29.7k11 gold badges96 silver badges104 bronze badges

answered Nov 29, 2017 at 6:54

Suren Srapyan

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4 Comments

user3013494 Over a year ago

I don't understand how to fix it. If I redefine it var aa = a, it doesn't work too.

Suren Srapyan Over a year ago

You need to copy the actual object to which a refers - into another object which { ...a } does. var aa = a is just another reference to the actual object. I think you need to look at objects and how they are stored in the memory

briosheje Over a year ago

Worth noting that Object destructing has a quite limited support at the current state.

Suren Srapyan Over a year ago

Instead you can use Object.assign

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