Javascript - check for variable

Question

here is a very nooby question for which answer I searched way too long while not finding anything. I'm not used to javascript but other programming languages so, how does it work if you want something to be constantly checked for?

Here my code:

var test = 0;

$( ".test_div" ).click(function() {
    test = 1;
});

Now if I want to check if the variable is 1, constantly, what do I do? I tried this but it didn't work:

if (test == 1) { }

Thanks!

You can't constantly check something as javascript runs on a single thread (if you do something without pause, nothing else will run), but you can check it regularly. Look into the setInterval function, or Object.observe as recommended below. — doldt
– doldt, Commented May 8, 2015 at 8:06
Do take into consideration that the Object.observe function is experimental, it might not be compatible with all the browsers... — Tom
– Tom, Commented May 8, 2015 at 8:08
I see! Thanks everyone. @Mr. Alien - Well, I thought of it more like Java, in which it's running through the whole code all the time, if you know what I mean. — wupto
– wupto, Commented May 8, 2015 at 8:11

Cagatay Ulubay · Accepted Answer · 2015-05-08 08:10:18Z

You are searching for something do be done in an interval

Following could help you:

var test = 0;
var interval;

function check_test() {
    if( test == 1 ){
        clearInterval( interval );
        console.log( "Test is 1 now!" );
    }
}

interval = window.setInterval( check_test, 1000 );

The 1000 is in milliseconds, so 1000 ms = 1 second. This will call check_test() every 1sec.

You also could do window.setTimeout in a simmiliar way, but this will do it just one time. Than you could call it inside the function again and if you want to stop it, you just stop calling it.

Jonathan Smith · Accepted Answer · 2015-05-08 08:06:32Z

1

If you are using Chrome or Opera, have a look at Javascript Object.observe()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/observe

If you need something less bleeding-edge, you would need to use a framework (such as Angular, although others are available) where you can set watches on variables.

answered May 8, 2015 at 8:06

Jonathan Smith

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2 Comments

Jeremy Thille Over a year ago

...or setInterval as a dirty workaround, as Doldt suggested in comments.

Jonathan Smith Over a year ago

Where is your sense of adventure? :o)

atulmy · Accepted Answer · 2015-05-08 08:13:02Z

There are several ways you can check if the value has changed.

Using setInterval method:

    var test = 0; // initial value
    var checkInterval = 1000; // time in millisecond, 1000 = 1 second

    setInterval(function() {
        if(test !== 0) { // check if test is not equal to initial value
            console.log("Test value changed! New value: "+test);
        }
    }, checkInterval);

The above code will test the condition every 1 second.

Roy Miloh · Accepted Answer · 2015-05-08 08:32:23Z

0

I'll take you a little bit back, do you really need to check it constantly? even if there are known specific events when it's value can be changed? I think it depends on your needs.

First of all, I would consider Pub/Sub or Observer patterns, they would be definitely more efficient and reliable than running a special interval each X milliseconds.

answered May 8, 2015 at 8:32

Roy Miloh

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