What is [1,2,3,4][1,2] in javascript

Question

can anyone explains the above question with explanation. I tried it console and the answer coming is 3

[1,2,3,4][1,2] //consoles 3

Answer 1

The first [1,2,3,4] is an array of 4 numbers.

The second [1,2] is a bracket notation (used here to access an item of the above array).

Inside that bracket notation you have a comma operator that evaluates to its right most expression 2.

So:

[1,2,3,4][1,2]

is the same as:

[1,2,3,4][2]

which is the same as:

var arr = [1,2,3,4];
arr[2];

Answer 2

[1,2,3,4] is an array literal.

1,2 is two numbers with a comma operator between them, so resolves to 2.

So you are getting index 2 (the third item) from the array.

var array = [1,2,3,4];
var property = (1,2);
var result = array[property];

console.log({ array: array, property: property, result: result });

Answer 3

It's an immediately invoked array with a comma operator

The comma operator evaluates each of its operands (from left to right) and returns the value of the last operand.

for the index.

[1, 2, 3, 4][1, 2]

resolves to

[1, 2, 3, 4][2] // 3