List properties with empty (undefined) values in JavaScript object

Question

If I have a JavaScript object:

var object = {
  propertyOne: undefined,
  propertyTwo: 'defined',
  propertyThree: 'defined',
  propertyFour: undefined
}

How can I create a method that will list the properties with undefined values (in the example's case, propertyOne and propertyFour).

I'm quite new to JavaScript, and this is what I had so far:

function getEmptyProperties(object) {
  var emptyProps = [];
  for (var property in object) {
    if (object.property === undefined) {
      emptyProps += property
    }
  }
  return emptyProps
}

But this returns ALL of the properties, regardless if they are undefined or not.

I know I'm missing some things that are principal in JS, but can't figure it out. Kindly help please?

Sze-Hung Daniel Tsui · Accepted Answer · 2015-05-30 05:44:09Z

3

Iterate over the object with:

Object.keys(object).forEach(function(val, i){
  if (object[val] === undefined){
  //do things to save the properties you want to save or delete
  }
})

For fundamentals I might suggest Eloquent JavaScript. It's free. You have a number of syntax errors in your code that could be fixed if you read the first 6ish chapters.

answered May 30, 2015 at 5:44

Sze-Hung Daniel Tsui

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Comments

Pavan Ravipati · Accepted Answer · 2015-05-30 05:42:40Z

0

var getEmptyProperties = function(object) {
  var emptyProps = [];
  for (var property in object) {
    if (object[property] === undefined) {
      emptyProps.push(property);
    }
  }
  return emptyProps
}

answered May 30, 2015 at 5:42

Pavan Ravipati

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1 Comment

SeinopSys Over a year ago

You should explain what this code does and how, so it's easier to understand.

score 0 · Accepted Answer · 2015-05-30 06:17:31Z

0

You may use filter, to get an array of only the properties that are undefined:

var obj = {
    propertyOne: undefined,
    propertyTwo: 'defined',
    propertyThree: 'defined',
    propertyFour: undefined
};

var undefProps = Object.keys(obj).filter(function (key) {
    return obj[key] === undefined;
});

// undefProps: ["propertyOne", "propertyFour"]

And with an arrow function!:

var undefProps = Object.keys(obj).filter(k => obj[k] === undefined);

edited May 30, 2015 at 6:17

answered May 30, 2015 at 6:00

user4698813

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