Can the IF statement be used instead of WHILE loop in this script?

Question

I'm learning JavaScript with the help of a number of books. In one of them I came up with a script that displays a couple of flags and then you click on them to randomly change them:

var myImages = new Array("usa.gif","canada.gif","jamaica.gif","mexico.gif");

function changeImg(that) {
        var newImgNumber = Math.round(Math.random() * 3);

        while (that.src.indexOf(myImages[newImgNumber]) != -1)
        {
            newImgNumber = Math.round(Math.random() * 3);
        }

        that.src = myImages[newImgNumber];
        return false;
}

It has a while loop to make sure that when you click on a flag you don't end up with the same one. The rest of the code in HTML looks like this:

<body>
    <img name="img0" src="usa.gif" border="0" onclick="return changeImg(this)" />
    <img name="img1" src="mexico.gif" border="0" onclick="return changeImg(this)" />
</body>

Now, my question is, if I use an IF statement instead of a while loop, apparently the code works the same. In this particular example why is the while loop used instead of IF? Thanks.

There's a small chance that a single re-try will pick the same number again, so the `while` loop lets the function keep trying repeatedly. — Pointy, Sep 24 '15 at 19:23
You use "if" over while only when you are not expecting multiple outcomes. — Techidiot, Sep 24 '15 at 19:25

score 6 · Accepted Answer · answered Sep 24 '15 at 19:23

The while statement basically translates as "while the number I've chosen matches the index of the image already in the current image tag, continue". So while an if statement may work most of the time, it's possible that your random number generator could generate, say, the number 0 multiple times in a row when you click on img0. while ensures that eventually you'll get a new image.

score 3 · Answer 2 · answered Sep 24 '15 at 19:23

3

There's a random number involved; you could get the same random number twice in a row.

Checking once is insufficient–the next number generated could be the same.

answered Sep 24 '15 at 19:23

Dave Newton

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score 1 · Answer 3 · answered Sep 24 '15 at 19:24

1

No because you could choose the same one twice in a row since you are using random numbers.

answered Sep 24 '15 at 19:24

Wowsk

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score 1 · Answer 4 · edited May 23 '17 at 12:14

1

Your goal is to make a random shuffle. Try to read answers to that question: How to randomize (shuffle) a JavaScript array?

edited May 23 '17 at 12:14

Community

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answered Sep 24 '15 at 19:33

Schullz

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OP's goal was to understand the JS code in the book, I think? – Dave Newton Sep 24 '15 at 19:45
Yes, thank you. Evidently I'm new at coding and I'm just trying to understand the logic behind the statements by asking "what if i used this instead of that". – rohn Sep 24 '15 at 20:32

Can the IF statement be used instead of WHILE loop in this script?

4 Answers4