What Removing Object Properties Tells Us About JavaScript — Smashing Magazine

A group of contestants are asked to complete the following task:

Make object1 similar to object2.

let object1 = { a: "hello", b: "world", c: "!!!", }; let object2 = { a: "hello", b: "world", };

Seems easy, right? Simply delete the c property to match object2. Surprisingly, each person described a different solution:

• Contestant A: “I set c to undefined.”
• Contestant B: “I used the delete operator.”
• Contestant C: “I deleted the property through a Proxy object.”
• Contestant D: “I avoided mutation by using object destructuring.”
• Contestant E: “I used JSON.stringify and JSON.parse.”
• Contestant F: “We rely on Lodash at my company.”

An awful lot of answers were given, and they all seem to be valid options. So, who is “right”? Let’s dissect each approach.

Contestant A: “I Set c To undefined.”

In JavaScript, accessing a non-existing property returns undefined.

const movie = { name: "Up", }; console.log(movie.premiere); // undefined

It’s easy to think that setting a property to undefined removes it from the object. But if we try to do that, we will observe a small but important detail:

const movie = { name: "Up", premiere: 2009, }; movie.premiere = undefined; console.log(movie);

Here is the output we get back:

{name: 'up',...