Javascript: Where do I put Math.floor(Math.random)?

Question

Okay, I'm obviously an extreme newbie, so be gentle. As I'm learning Javascript, I'm creating a quiz to better help me retain and practice the information. The following is a sample of my code so far(the actual array has been shortened for this question).

I works fine for what it is at this point in my learning progress, except that I can't seem to use Math.floor(Math.random()) to create a non-linear q & a experience.

var qAndA = [["What starts a variable?", "var"], 
["What creates a popup with text and an OK button?", "alert()"],  
["What is the sign for a modulo?", "%"]];
function askQuestion(qAndA) {
    var answer = prompt(qAndA[0], " ");    
    if (answer === qAndA[1]) { 
        alert("yes");
    } else {
        alert("No, the answer is " + qAndA[1]);
    }
}
for (i = 0; i < qAndA.length; i++) {
    askQuestion(qAndA[i]);
}

I've looked at all the potential answers here and elsewhere, but nothing addresses this speicific point.

Can anyone out there help me?

possible duplicate of [How to randomize (shuffle) a javascript array?](http://stackoverflow.com/questions/2450954/how-to-randomize-shuffle-a-javascript-array) — nmaier, Jun 28 '14 at 20:30
That was good to know. But for my purposes, the simpler approach works best. — user3786587, Jun 30 '14 at 08:57

score 1 · Accepted Answer · answered Jun 28 '14 at 20:32

Easiest way to select a random element in an array:

var randomIndex = Math.floor(Math.random() * qAndA.length)
var randomQuestion = qAndA[randomIndex]

Now put that in a loop:

var questionsToAsk = qAndA.length
for (i = 0; i < questionsToAsk; i++) {
    var randomIndex = Math.floor(Math.random() * qAndA.length)
    var randomQuestion = qAndA[randomIndex]
    askQuestion(randomQuestion);
}

score 0 · Answer 2 · answered Apr 06 '17 at 23:23

It's faster to use | 0 as in

const randomIndex = Math.random() * qAndA.length | 0;
const randomQuestion = qAndA[randomIndex];

The | 0 is a binary or of 0 which the JavaScript spec effectively says the result is converted to an integer before the | happens. Note that | 0 is not the same as Math.floor. | 0 rounds to 0 whereas Math.floor rounds down.

         | 0   Math.floor         
------+------+------------
  2.5 |   2  |   2
  1.5 |   1  |   1
  0.5 |   0  |   0
 -0.5 |   0  |  -1
 -1.5 |  =1  |  -2
 -2.5 |  -2  |  -3

Javascript: Where do I put Math.floor(Math.random)?

2 Answers2