I am so confused about Object in JavaScript

Question

I am a newbie to JavaScript, but I am familiar with Python. I am trying to figure out the differences between the Dictionary in Python and the Object in JS.

As far as I know, the key in a dictionary in Python needs to be defined in advance, but it could be undefined in an object in JS. However, I am confused about those cases:

var n = 'name';
var n2 = n;
var person = {n: 'mike'};

person.n    # 'mike'
person['n'] # 'mike'
person[n2]  # undefined
person.n2   # undefined
person['name']  # undefined
person.'name'  # undefined

I am so confused that why those three variables n, n2 and name are not equal, because compared with that in Python:

n = 'name'
n2 = n
person = {n:'mike'}

person[n]  # 'mike'
person[n2] # 'mike'
person['name'] # 'mike'

I guess that might due to the fact that in Python, n and n2 both point to the unique string object 'name', so they are the same. But could someone explain the mechanism behind in JS to me?

Answer 1

When you assign like:

var person = {n: 'mike'};

The n is not referencing to the variable but it's own property. If you need to reference the variable you will need to use bracket notation like:

var person = {[n]: 'mike'};

For more information about bracket notation, see computed property.

In JavaScript, the use of quote for property is same without using quote:

var person = {n: 'mike'};
var person = {'n': 'mike'}; // same as above

But if you define property like giving space:

var person = {my property: 'mike'}; // invalid

In this case, you must need to use the quote:

var person = {'my property': 'mike'};