Use Square Bracket Notation for headache-free coding

Ok! So this happened! I failed an interview because I overlooked the basic!

There are two ways to access property values of an object in javascript:

1. Dot notation ( user.name )
2. Square Bracket notation ( user["name"])

And most of the time, property names are known and simple and dot notation comes naturally to many of us.

But there is a catch. Read on!

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Objects

TL;TR -

Square bracket notation saved you from breaking your head compared to dot notation.
When you defined a key into a variable and wants to add it as new property into an object, it will only work if square bracket notation is used.

let user = {
  name: "John",
  age: 30
};
let key = "gender";
user.key = "male";
alert( user.gender ) // undefined
user[key] = "male";
alert( user.gender ) // male

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Use dot notation:
When an object is already defined and you just want to read the property provided all property are single word.
Single word: "name"

Avoid dot notation:
When an object is already defined and you just want to read the property but few or all property are multiword.
multiword: "first name"

let user = {
  name: "John",
  age: 30,
  "likes birds": true  // multiword property name must be  quoted
};

user.likes birds = true // this would give a syntax error

Use square bracket notation:
I mean in all case (at least from what I know, feel free to comment )

few examples: Works for all operators like charm

let user = {};

// set
user["likes birds"] = true;

// get
alert(user["likes birds"]); // true

// delete
delete user["likes birds"];

Avoid square bracket notation:

Guess we'll never know....

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Read more about Objects

Comments

[Talha Altınel]

nice nuance to point out, but it comes down to the developer choice, there is no right or wrong, since ES spec defines JSON objects as a class and a map at the same time. Generally it is considered bad practice to put blank spaces in your keys. If you need a map, use it is a map, if you need a class, use it as a class.

[Yanger Rai]

Indeed. No right or wrong way but preferences