Removing falsies from JavaScript object

Question

So I write a short function to remove members from an object that have falsy values:

for (var key in object) {
    if (!object[key]) {
        delete object[key];
    }
}

A couple days later I check source control and someone has changed this to:

var newObject = {};
for (var key in object) {
    if (object[key]) { newObject[key] = object[key]; }
}
return newObject;

There's no comments on the check-in and the guy is not here today at work.

Which implementation is better? What are the performance implications of each method?

Yacoby · Accepted Answer · 2010-07-21 21:58:11Z

3

You cannot delete a property on an object that it inherits from a prototype. So in some cases your code may fail to work as expected.

Source

answered Jul 21, 2010 at 21:58

Yacoby

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Comments

Daniel Vassallo · Accepted Answer · 2010-07-21 21:58:23Z

2

You cannot delete a property of an object that it inherits from a prototype (although you can delete it directly on the prototype).

In the second example, a falsy property inherited from a prototype will not be copied to the newObject.

Comments

Tommy Stanton · Accepted Answer · 2016-04-13 17:29:06Z

1

Using Lo-Dash, consider this implementation (using _.pick):

var newObject = _.pick(object, function onlyTruthy(val, key) {
  return !!val;
});

edited Apr 13, 2016 at 17:29

answered Aug 15, 2014 at 22:09

Tommy Stanton

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Comments

Joe Martinez · Accepted Answer · 2010-07-21 21:58:25Z

0

I think your code reads much more intuitively. Maybe he just didn't want to change the original object?

answered Jul 21, 2010 at 21:58

Joe Martinez

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2 Comments

Marcel Korpel Over a year ago

Not true, see Daniel's and Yacoby's answers.

Joe Martinez Over a year ago

Those answers and mine are not mutually exclusive. Well, at least they may not be. We don't have enough context to make a determination.

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