Methods and Applications of jQuery to Retrieve All CSS Styles of an Element

Introduction

In web development, there are scenarios where one needs to copy all CSS styles from one element to another dynamically. This is particularly useful when styles are defined in external stylesheets, making direct access via the style attribute insufficient. jQuery, a popular JavaScript library, simplifies DOM manipulation but does not provide a built-in method to retrieve all computed styles. This article addresses this gap by presenting a custom solution.

Core Solution: Custom jQuery Function to Get All CSS Styles

Based on the best answer from the provided Q&A, a function named css() is designed to retrieve both inline and external styles. The function iterates through all document.styleSheets, extracts rules, and matches selectors to the target element.

function css(a) {
    var sheets = document.styleSheets, o = {};
    for (var i in sheets) {
        var rules = sheets[i].rules || sheets[i].cssRules;
        for (var r in rules) {
            if (a.is(rules[r].selectorText)) {
                o = $.extend(o, css2json(rules[r].style), css2json(a.attr('style')));
            }
        }
    }
    return o;
}

Here, css2json() converts CSS styles to a JSON object for easy manipulation.

Code Explanation and Implementation

The css2json() function handles both CSSStyleDeclaration objects and string representations of CSS. It normalizes property names to lowercase for consistency.

function css2json(css) {
    var s = {};
    if (!css) return s;
    if (css instanceof CSSStyleDeclaration) {
        for (var i in css) {
            if ((css[i]).toLowerCase) {
                s[(css[i]).toLowerCase()] = (css[css[i]]);
            }
        }
    } else if (typeof css == "string") {
        css = css.split("; ");
        for (var i in css) {
            var l = css[i].split(": ");
            s[l[0].toLowerCase()] = (l[1]);
        }
    }
    return s;
}

To use this, pass a jQuery object to css(), and apply the returned object with jQuery's css() method.

var style = css($("#elementToGetAllCSS"));
$("#elementToPutStyleInto").css(style);

Alternative Approach: jQuery Plugin

As a supplementary reference, Answer 2 introduces a jQuery plugin getStyleObject.js that uses window.getComputedStyle for broader browser compatibility, including IE. This plugin retrieves all possible styles, including vendor-specific properties.

jQuery.fn.getStyleObject = function(){
    // code as provided
}

Basic usage involves calling copyCSS() to transfer styles between elements.

Applications and Best Practices

This technique is valuable for dynamic styling, theme switching, or cloning element appearances. However, it can be performance-intensive due to iterating through all stylesheets. Use it judiciously and consider caching results for repeated use.

Conclusion

By leveraging jQuery and custom functions, developers can effectively retrieve and apply all CSS styles from elements, overcoming limitations of external stylesheets. The presented solution offers a practical approach for various web development tasks.