Accessing Object Properties with Variables - bracket

JavaScript
1

Tell us what’s happening:
I cannot explain why I have to use the bracket notation in
var player = testObj[playerNumber];

in the first tentative, I have used parenthesis, and it doesn’t work (obvious!). But why I have to use brackets? is there any additional concept, or should I just remember it by heart?

Many many thanks

Your code so far


// Setup
var testObj = {
  12: "Namath",
  16: "Montana",
  19: "Unitas"
};

// Only change code below this line;

var playerNumber=16;       // Change this Line
var player = testObj[playerNumber];   // Change this Lin

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0 Safari/605.1.15.

Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/basic-javascript/accessing-object-properties-with-variables

3

in a very simplified way, I will have parenthesis in functions to create actions, while I will have to use brackets to point or reference? could it be said in that way?
Many thanks!

4

Whenever you use dot notation, it looks for property within your object, so:

const obj = {
  a: 1,
  b: 2,
  c: 3
};

const a = 'b';

console.log(obj.a) // 1
console.log(obj[a]) // 2
console.log(obj['a']) // 1

// ...so:
obj.a === obj['a'];
obj.a !== obj[a];
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