javascript multiple object instance same timestamp

Question

I am curious why this returns the same timestamp for each. The object should have different identifiers I would think.?

/js/helpers/v01.js

var Tester = (function () {
    var object_id = 'Tester';
    var object_id_unique = (new Date().getTime()) + '-' + (new Date().getMilliseconds());
    var _this;

    /**
     *
     * @constructor
     */
    function Tester(obj_name) {
        this.name = obj_name;
        this.run();
    }

    Tester.prototype = {

        run: function () {
            "use strict";
            var $body = document.getElementsByTagName('body')[0];
            var $node = document.createElement('div');
            $node.innerHTML = '<lable>' + this.name + ': </lable>' + ' ' + object_id + '-' + object_id_unique;
            $body.appendChild($node);
        }
    };
    return Tester;
})();

Here is the page

<!DOCTYPE html>
<html lang="en">
<head>
<script type="text/javascript" src="/js/helpers/v01.js"></script>
</head>
<body>

<script type="text/javascript">
    new Tester('A');
    setTimeout(function () {
        new Tester('B');
    }, 500);
</script>
</body>
</html>

My output return this

A: Tester-1385613846838-838
B: Tester-1385613846838-838

Put console.log('foo') before var object_id_unique = ...; and see how often it executes. I recommend to learn how to debug JavaScript so that you can set breakpoints, inspect variables etc. — Felix Kling
– Felix Kling, Commented Nov 28, 2013 at 5:12

Qantas 94 Heavy · Accepted Answer · 2013-11-28 05:09:31Z

1

In your closure you're permanently setting the value of object_id_unique (as the function is called immediately upon definition, not when you call the returned function) - move that inside the returned function. This should fix it:

var Tester = (function () {
    var object_id = 'Tester';
    var _this;

    /**
     *
     * @constructor
     */
    function Tester(obj_name) {
        this.name = obj_name;
        this.run();
    }

    Tester.prototype = {

        run: function () {
            "use strict";
            var object_id_unique = (new Date().getTime()) + '-' + (new Date().getMilliseconds());
            var $body = document.getElementsByTagName('body')[0];
            var $node = document.createElement('div');
            $node.innerHTML = '<lable>' + this.name + ': </lable>' + ' ' + object_id + '-' + object_id_unique;
            $body.appendChild($node);
        }
    };
    return Tester;
})();

answered Nov 28, 2013 at 5:09

Qantas 94 Heavy

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1 Comment

Jon C. Over a year ago

Thank you, makes sense. I had multiple objects like this one and was scratching my head why there the same... got it.

Barmar · Accepted Answer · 2013-11-28 05:09:44Z

1

You're only creating object_id_unique once, when you define the class. If you want it to be different in each instance, you need to assign it in the constructor.

answered Nov 28, 2013 at 5:09

Barmar

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