How to Extract CSS Properties Dynamically Using JavaScript?

Extracting CSS Properties Using JavaScript

Navigating the stylesheets attached to an HTML document can provide valuable insights into the presentation of page elements. In particular, the ability to read specific CSS properties can assist in dynamic style manipulation.

One approach involves manually inspecting the document.styleSheets object and parsing the style rules. However, this method is labor-intensive and can become unwieldy, especially when targeting specific selectors.

A more direct technique is to create a temporary element that matches the desired selector. Using the getComputedStyle() (for modern browsers) or currentStyle (for Internet Explorer) methods, you can retrieve the computed value of any CSS property for the created element.

For instance, consider the following code to retrieve the color property of a

with the class "layout":

<code class="javascript">function getStyleProp(elem, prop) {
  if (window.getComputedStyle) {
    return window.getComputedStyle(elem, null).getPropertyValue(prop);
  } else if (elem.currentStyle) {
    return elem.currentStyle[prop]; // IE
  }
}
window.onload = function () {
  var d = document.createElement("div"); // Create div
  d.className = "layout"; // Set class = "layout"
  alert(getStyleProp(d, "color")); // Get property value
};</code>

Alternatively, if you want to determine the CSS property inherited from a stylesheet without considering any inline styles, the following function can be used:

<code class="javascript">function getNonInlineStyle(elem, prop) {
  var style = elem.cssText; // Cache the inline style
  elem.cssText = ""; // Remove all inline styles
  var inheritedPropValue = getStyleProp(elem, prop); // Get inherited value
  elem.cssText = style; // Add the inline style back
  return inheritedPropValue;
}</code>

By leveraging these techniques, developers can dynamically adjust the CSS properties of elements, manipulate their presentation, and gain a deeper understanding of the page's styling.

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