Javascript – Object doesn’t support this property or method javascript error in IE6 only

internet-explorer-6javascriptobject

I've searched the internet and this great stackoverflow.com site particularly, but cannot help myself. I am not very experienced programmer and a friend of mine asked me to fix the bug that is on IE6 only. It works on FF, IE7/8, Opera.
Here is the PART of the code that gives error message on IE6:

(function(d, n, r) {
  var ie, jscript, settings = {};
  function add(element, type, listener) { element.addEventListener(type, listener, false); };
  function remove(element, type, listener) { element.removeEventListener(type, listener, false); };
  var l = {change:[], ready:[], load:[]};
  a11y = function(f) {
    a11y.change(f);
  };
})
(self.document, self.navigator);

The error is on line 7: a11y.change(f); All other browsers are OK, just IE6. I am not author of the script, just trying to fix this. Can anybody help, please? There must be some problem with function declaration or…?

Best Answer

The example looks pretty confused there is a lot of code there that looks to be a distraction.

From what I can see the problem is in this code:

a11y = function(f) {
    a11y.change(f);
};

Here you are defining a new function called a11y and inside the definition of that function you are calling a method 'change' on the function a11y being defined. I'm surprised that works in any browser.

Related Solutions

Javascript – Why doesn’t JavaScript support multithreading

JavaScript does not support multi-threading because the JavaScript interpreter in the browser is a single thread (AFAIK). Even Google Chrome will not let a single web page’s JavaScript run concurrently because this would cause massive concurrency issues in existing web pages. All Chrome does is separate multiple components (different tabs, plug-ins, etcetera) into separate processes, but I can’t imagine a single page having more than one JavaScript thread.

You can however use, as was suggested, setTimeout to allow some sort of scheduling and “fake” concurrency. This causes the browser to regain control of the rendering thread, and start the JavaScript code supplied to setTimeout after the given number of milliseconds. This is very useful if you want to allow the viewport (what you see) to refresh while performing operations on it. Just looping through e.g. coordinates and updating an element accordingly will just let you see the start and end positions, and nothing in between.

We use an abstraction library in JavaScript that allows us to create processes and threads which are all managed by the same JavaScript interpreter. This allows us to run actions in the following manner:

Process A, Thread 1
Process A, Thread 2
Process B, Thread 1
Process A, Thread 3
Process A, Thread 4
Process B, Thread 2
Pause Process A
Process B, Thread 3
Process B, Thread 4
Process B, Thread 5
Start Process A
Process A, Thread 5

This allows some form of scheduling and fakes parallelism, starting and stopping of threads, etcetera, but it will not be true multi-threading. I don’t think it will ever be implemented in the language itself, since true multi-threading is only useful if the browser can run a single page multi-threaded (or even more than one core), and the difficulties there are way larger than the extra possibilities.

For the future of JavaScript, check this out: https://developer.mozilla.org/presentations/xtech2006/javascript/

Javascript – How to check if an object has a specific property in JavaScript

I'm really confused by the answers that have been given - most of them are just outright incorrect. Of course you can have object properties that have undefined, null, or false values. So simply reducing the property check to typeof this[property] or, even worse, x.key will give you completely misleading results.

It depends on what you're looking for. If you want to know if an object physically contains a property (and it is not coming from somewhere up on the prototype chain) then object.hasOwnProperty is the way to go. All modern browsers support it. (It was missing in older versions of Safari - 2.0.1 and older - but those versions of the browser are rarely used any more.)

If what you're looking for is if an object has a property on it that is iterable (when you iterate over the properties of the object, it will appear) then doing: prop in object will give you your desired effect.

Since using hasOwnProperty is probably what you want, and considering that you may want a fallback method, I present to you the following solution:

var obj = {
    a: undefined,
    b: null,
    c: false
};

// a, b, c all found
for ( var prop in obj ) {
    document.writeln( "Object1: " + prop );
}

function Class(){
    this.a = undefined;
    this.b = null;
    this.c = false;
}

Class.prototype = {
    a: undefined,
    b: true,
    c: true,
    d: true,
    e: true
};

var obj2 = new Class();

// a, b, c, d, e found
for ( var prop in obj2 ) {
    document.writeln( "Object2: " + prop );
}

function hasOwnProperty(obj, prop) {
    var proto = obj.__proto__ || obj.constructor.prototype;
    return (prop in obj) &&
        (!(prop in proto) || proto[prop] !== obj[prop]);
}

if ( Object.prototype.hasOwnProperty ) {
    var hasOwnProperty = function(obj, prop) {
        return obj.hasOwnProperty(prop);
    }
}

// a, b, c found in modern browsers
// b, c found in Safari 2.0.1 and older
for ( var prop in obj2 ) {
    if ( hasOwnProperty(obj2, prop) ) {
        document.writeln( "Object2 w/ hasOwn: " + prop );
    }
}

The above is a working, cross-browser, solution to hasOwnProperty, with one caveat: It is unable to distinguish between cases where an identical property is on the prototype and on the instance - it just assumes that it's coming from the prototype. You could shift it to be more lenient or strict, based upon your situation, but at the very least this should be more helpful.

Best Answer

Related Solutions

Javascript – Why doesn’t JavaScript support multithreading

Javascript – How to check if an object has a specific property in JavaScript

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