JS/Jquery variable schange event [duplicate]

This question already has answers here: Closed 11 years ago.

Possible Duplicate:

detect variable change in javascript

How can i found out that my variable has changed?

I h开发者_如何学Goave an event that performed every time when my variable is for example == 1, i want it to perfome only when my variable changes.

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You can do that via a property setter, which is a newly-standardized part of the language (new as of the ECMAScript5 specification). That will only work for a property defined with a setter on an object, not with any old variable or property.

Here's an example of an object with a foo property with both a getter and a setter:

var obj = {};
Object.defineProperty(obj, "foo", (function(){
  var value = 42;

  function fooGet() {
    display("Getting: " + value);
    return value;
  }
  function fooSet(newValue) {
    display("Setting: " + newValue);
    value = newValue;
  }

  return {
    get: fooGet,
    set: fooSet
  };
})());

Live example, but only works on browsers with support for ECMAScript5 properties, which I think is just Google Chrome at the moment

Or of course, just directly use getter and setter functions rather than properties. :-)

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Simple: Don't use a primitive variable but an object which has a "setter" method to change the value. In the setter, you can call additional code.

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You can't do this with primitives. The only way it would be possible is if you encapsulated the variable in an object, and added some custom events to this object.

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@T.J. I think @Aaron is suggesting an object that does something like this:

var myVar = new Watched(1, function (newValue) { alert(newValue) });

myVar.add(2); // alert(3);
myVar.add(10); // alert(13)

Where Watched maintains an internal value that is updated by methods, which fire a callback to say they have updated.

EDITED:

Ok maybe not what @Aaron was thinking:)

I had something very simple like this in mind:

function Watched (initVal, cb) {
    var value = initVal;

    function add (val) {
        value += val;
        cb(value);
    }

    // return public methods
    return { add: add };
}

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You could use the setInterval method to periodically check the variable's value and do your stuff if it's what you want.

It's not a nice solution, though. The other suggestions are better.

http://www.elated.com/articles/javascript-timers-with-settimeout-and-setinterval/

EDIT:

var myVar = 0;

var intervalId = setInterval('checkVariable(myVar);', 3000);

function checkVariable(theVar) {
    if (theVar == 1) {
        alert('Variable is 1.');
    }
}

That will execute checkVariable(myVar) every 3 seconds.