Keeping only certain properties in a JavaScript object

Question

I have an object. I would like to modify the object (not clone it) by removing all properties except for certain specific properties. For instance, if I started with this o

Answer 1

Pass a map of whitelisted keys into an IIFE (immediately invoked function expression); not just elegant but also flexible IMO (especially if moved off into a function not unlike in Juan Mendes' answer)

var myObj={
    p1:123,
    p2:321,
    p3:{p3_1:1231,p3_2:342},
    p4:'23423',
    //....
    p99:{p99_1:'sadf',p99_2:234},
    p100:3434
}

var myObj = (function(origObj, whiteListMap) {
    for (var prop in origObj) {
        if (!whiteListMap[prop]) {
            delete origObj[prop];
        }
    }
    return myObj;
})(myObj, {'p1': 1, 'p2': 1, 'p100': 1});

console.log(JSON.stringify(myObj)); //{"p1":123,"p2":321,"p100":3434}

Answer 2

This was the first hit when googling 'js keep only certain keys' so might be worth an update.

The most 'elegant' solution might just be using underscore.js

_.pick(myObj, 'p1', 'p2', 'p100')

Answer 3

Just re-initialise the object:

myObj = {
    p1:   myObj.p1,
    p2:   myObj.p2,
    p100: myObj.p100
};

Another way is to delete certain properties, which is less effective:

var prop = ['p1', 'p2', 'p100'];
for (var k in myObj) {
    if (prop.indexOf(k) < 0) {
        delete myObj[k];
    }
}

Answer 4

I suppose you could add a new method to the prototype:

if (!('keepOnlyTheseProps' in Object.prototype)) {
  Object.prototype.keepOnlyTheseProps = function (arr) {
    var keys = Object.keys(this);
    for (var i = 0, l = keys.length; i < l; i++) {
      if (arr.indexOf(keys[i]) < 0) delete this[keys[i]];
    }
  }
}

myObj.keepOnlyTheseProps(['p1', 'p2', 'p100']);

Fiddle.

Answer 5

I Made this short solution for case where I have an array with objects.

so consider the array below?

arr=[{"a1":"A1","b1":"B1"},{"a1":"Z1","b1":"X1"}];
console.log(arr);

I want to keep only "b1" properties of all objects.

You can use map() and delete for that as follows:

arr=[{"a1":"A1","b1":"B1"},{"a1":"Z1","b1":"X1"}];
arr=arr.map(function(d){
        delete d["a1"];
        return d;

    });
console.log(arr);

result is an array with objects but only "b1" properties.

Answer 6

var myObj = {a: 1, b: 2, c:3};

function keepProps(obj, keep) {
    for (var prop in obj) {
        if (keep.indexOf( prop ) == -1) {
            delete obj[prop];
        }             
    }
}

keepProps(myObj, ['a', 'b']);
console.log(myObj);

http://jsfiddle.net/mendesjuan/d8Sp3/2/