Picking 2 random elements from array

Question

What is the most efficient way to select 2 unique random elements from an array (ie, make sure the same element is not selected twice).

I have so far:

var elem1;
var elem2;

elem1 = elemList[Math.ceil(Math.random() * elemList.length)];
do {
  elem2 = elemList[Math.ceil(Math.random() * elemList.length)];
} while(elem1 == elem2)

But this often hangs my page load.

Any better solution?

Extra question, how do I extend this to n elements

Answer 1

do NOT use loops and comparisons. Instead

• shuffle the array
• take first two elements

Answer 2

It can be done using built-in functionality (slice and sort),

var n = 2
    randomItems = array.sort(() => .5 - Math.random()).slice(0, n);