Vacheslav Starikov's » javascript

cssRules null in Chrome

Vacheslav — Thu, 01 Mar 2012 15:28:44 +0000

I found this problem when tryed to use cssRules of document.styleSheets[i] locally in Chrome but found that cssRules is null and only in Chrome. I need only to add some rules but not to read or modify existed rules so this fix is not for all.

Here’s the bug http://code.google.com/p/chromium/issues/detail?id=49001.

And here’s my workaround for this problem:

var styles = document.styleSheets;
var style = null;
for (var s = 0; s < styles.length; s++)
    if(!styles[s].href) {
        style = styles[s];
        break;
    }
if (style == null)
    style = jQuery("")
        .appendTo('head').get(0);
var rules = style.cssRules; // is not null!!!

Accessing a dimensional array in JavaScript

Vacheslav — Thu, 31 Mar 2011 06:26:48 +0000

Let’s declare a two dimensional array and try to access the element. Here is the first example:

var array = [[1, 2, 3],[4, 5, 6]];
alert(array[1][1]);
// Output: 5

Here is the same sample but with another sytnax:

var array = new Array(2);
array[0] = new Array(3);
array[0][0] = 1;
array[0][1] = 2;
array[0][2] = 3;
array[1] = new Array(3);
array[1][0] = 4;
array[1][1] = 5;
array[1][2] = 6;
alert(array[1][1]);
// Output: 5

Again, another syntax of this example to access a javascript array:

var array = new Array(new Array(1, 2, 3), new Array(4, 5, 6));
alert(array[1][1]);
// Output: 5

Some developers make the following error when accessing a JavaScript array and wait that the 5 will be returned:

var array = [[1, 2, 3],[4, 5, 6]];
alert(array[1,1]);
// Output: [4, 5, 6]

JavaScript interpretes 1,1 as a comma separated expression and this expression returnes 1. Each part of the comma separated expression is executed left to right. The final value of the comma separated expression is the value of the last comma part. So, when you try to evaluate the following script in the sample below you will get the last array item because the value of the comma separated expression 0,1,2 will be 2:

var array = [1, 2, 3];
alert(array[0,1,2]);
// Output: 3

How to test for an empty javascript object

Vacheslav — Wed, 10 Mar 2010 08:43:16 +0000

Hi everybody! I’ve just had a discussion of how to test for an emtpy javascript object. As a result, I have several code snippets and I want to share them with You.

Problem

alert({}==null); // false
alert({}=={}); // false
alert({}=={}); // false
alert({}==0); // false
alert({}==""); // false
alert({}==[]); // false
// etc :)

So, none of the expressions above can check for an empty javascript object.

Pure javascript solution

function empty(o) {
    for(var i in o) 
        if(o.hasOwnProperty(i))
            return false;
 
    return true;
}

object.hasOwnProperty(property)	Returns a boolean indicating whether the object has the specified property. This method does not check down the object’s prototype chain. Learn details of hasOwnProperty here at developer.mozilla.org.

object.hasOwnProperty(property)

Returns a boolean indicating whether the object has the specified property. This method does not check down the object’s prototype chain.

Learn details of hasOwnProperty here at developer.mozilla.org.

JQuery + JQuery.JSON solution

var o = {};
alert($.toJSON(o)=='{}'); // true
 
var o = {a:1};
alert($.toJSON(o)=='{}'); // false

The code above simply converts an object to JSON string.

Your way

Well, if You have Your way of checking for an empty javascript object I am waiting Your comments! Thanks in advance!

Links

hasOwnProperty documentation

JQuery JavaScript Library

jquery-json plugin for JQuery