How do I remove a key from a JavaScript object? [duplicate]

Question

This question already has answers here:

How do I remove a property from a JavaScript object? (40 answers)

Closed 9 years ago.

Let's say we have an object with this format:

var thisIsObject= {
 'Cow' : 'Moo',
 'Cat' : 'Meow',
 'Dog' : 'Bark'
};

I wanted to do a function that removes by key:

removeFromObjectByKey('Cow');

• dst: Do you want the function to be a jQuery function or what does this have to do with jQuery?
• alex: That is actually a JavaScript object, associative arrays do not exist in JavaScript.
• thomasrutter: Yeah just some confusion with terminology I think, ie it's Javascript not Jquery, and it's an object not array (OP may come from other languages with associative arrays).

Answer 1

The delete operator allows you to remove a property from an object.

The following examples all do the same thing.

// Example 1
var key = "Cow";
delete thisIsObject[key]; 
// Example 2
delete thisIsObject["Cow"];
// Example 3
delete thisIsObject.Cow;

let animals = {
 'Cow': 'Moo',
 'Cat': 'Meow',
 'Dog': 'Bark'
};
delete animals.Cow;
delete animals['Dog'];
console.log(animals);

If you're interested, read Understanding Delete for an in-depth explanation.

• CMaury: If you are looping over keys in an object, and delete them if they match a certain value, does this affect the key index while you are looping over it?
• nullability: Beware that IE8 may throw an exception when using delete in certain circumstances. See stackoverflow.com/questions/1073414/…
• Ozymandias: Does anyone know the runtime of this operation?
• Randy Hall: In 10 years of JS-focused development in positions big and small, I have never once needed this before now or knew it existed. Thank you, kind sir, for this post.
• Ben174: If your linter is complaining about using the delete keyword, use: Reflect.deleteProperty(object1, 'property1');

Answer 2

If you are using Underscore.js or Lodash, there is a function 'omit' that will do it.
http://underscorejs.org/#omit

var thisIsObject= {
 'Cow' : 'Moo',
 'Cat' : 'Meow',
 'Dog' : 'Bark'
};
_.omit(thisIsObject,'Cow'); //It will return a new object
=> {'Cat' : 'Meow', 'Dog' : 'Bark'} //result

If you want to modify the current object, assign the returning object to the current object.

thisIsObject = _.omit(thisIsObject,'Cow');

With pure JavaScript, use:

delete thisIsObject['Cow'];

Another option with pure JavaScript.

thisIsObject = Object.keys(thisIsObject).filter(key =>
 key !== 'cow').reduce((obj, key) =>
 {
 obj[key] = thisIsObject[key];
 return obj;
 }, {}
);

• shabunc: Downvoted. The thing is that both in underscore and lodash _.omit returns new object, does not modify the current one. So, this is slightly a different thing.
• Mateusz Nowak: @shabunc The same with pure javascript. delete o.properrty does a lot more harm than good behind the scenes, as it changes o‘s hidden class and makes it a generic slow object.
• tonejac: object.property = undefined is legit. Worked perfectly! (upvoted)
• nanobar: Upvoted. A new immutable object is preferable in many cases.
• Patrik Beck: I am sorry for the downvote, but thisIsObject.cow = undefined; is very misleading. Object.keys(thisIsObject) will still pick up 'cow'. So it's not really deleted.

Answer 3

It's as easy as:

delete object.keyname;

or

delete object["keyname"];

• Sergii: If the key is generated number, and we does not know about it existing we can do next: const unknownKey = 100500; delete object[`${unknownKey}`];
• Afzal Ali: How this answer is different from first one?
• Leprosy: I just want to read @Sergii clarify this LOL
• Sergii: @Leprosy technically it's the same. But with unknown numbers as keys.