Conditional loop using if statement

Question

I'm learning some basic javascript, and would like to learn how to return to the beginning of a method when certain conditions are met.

In this scenario, the user must enter a character in the prompt in order to proceed to the statment "The character you typed was" string. I would like to implement a loop to send the program back to the start of the method if nothing is entered. I have the following, so far:

<script class="promptwindow">            
        var x
        x = prompt("Please type a character in the box and click OK", "")

        if (x = null)
            {****}

        document.write("The character you typed was ", x)    
</script>

I'm unsure what to use in the **** bracket, I need something similar to goto.

Edit: Yep, should have been ==. I'll leave the mistake there so that the comments make sense.

class="promptwindow" in script tag?

onetwo12
– onetwo12

2014-08-27 12:16:20 +00:00
Commented Aug 27, 2014 at 12:16 — onetwo12
– onetwo12, Commented Aug 27, 2014 at 12:16
no -> if (x = null) yes -> if (x == null)

Orelsanpls
– Orelsanpls

2014-08-27 12:17:31 +00:00
Commented Aug 27, 2014 at 12:17 — Orelsanpls
– Orelsanpls, Commented Aug 27, 2014 at 12:17

Fractaliste · Accepted Answer · 2014-08-27 12:39:09Z

3

To go back to the beginning of your function, just call it again:

<script type="text/javascript">
   ( function myFunction() {
        var x;
        x = prompt("Please type a character in the box and click OK", "")
        if (x === null)
            myFunction();
        document.write("The character you typed was ", x);
    })();
</script>

Be carreful to the document.write()'s position, when x will not be null anymore, all stacked document.write("The character you typed was ", x); will be executed

You can also use a loop...

<script type="text/javascript">
    function myFunction() {
        var x = null;
        while(x === null || x === ""){
            x = prompt("Please type a character in the box and click OK", "")
        }
        document.write("The character you typed was ", x);
    }
</script>

edited Aug 27, 2014 at 12:39

answered Aug 27, 2014 at 12:19

Fractaliste

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5 Comments

Wolfish Over a year ago

Brilliant! I was hoping for something like this, +1.

Wolfish Over a year ago

Erm... actually, this now does nothing at all. It's now just a blank page.

Fractaliste Over a year ago

@Wolfish Of course you have to call the function once to start it

Wolfish Over a year ago

Didn't seem to work. I'm using OnLoad in the <body> tag, but the loop doesn't seem to work. Edit: made the self-invocation work, but the loop is still broken.

Fractaliste Over a year ago

Actually prompts returns an empty string instead of null, the loop's condition should be updated

user3355403 · Accepted Answer · 2014-08-27 13:40:29Z

1

<script type = "text/JavaScript">
    function UserInput(_callback_)
    {
        var value = "";
        do
        {
            value = prompt("Please type a sentence in the box and click OK", "");
        }
        while(value === "");

        _callback_(value);
    }

    UserInput(function(text){
        document.write("The sentence you typed was { " + text + " }");
    });
</script>

http://jsfiddle.net/dqda8Lgk/

I hope it will help you :)

answered Aug 27, 2014 at 13:40

user3355403

1 Comment

Wolfish Over a year ago

This is a little more advanced, I'll be looking at callbacks later on today. I appreciate the snippet though, +1

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