CSSStyleSheet.insertRule() method inserts a new CSS rule into the current style sheet. (with some restrictions)

More specifically, though insertRule() is exclusively a method of the CSSStyleSheet, it actually inserts the rule into the CSSRuleList therein.

What the rule must contain depends on its type: For rule-sets the rule specifies both the selector and the style declaration. For at-rules, the rule specifies both the at-identifier and the rule content.


<var>stylesheet</var>.insertRule(<var>rule</var>, <var>index</var>)


  • rule is a DOMString containing the rule to be inserted,
    ...where rule specifies selector and declaration, or at-identifier and rule content.
  • index is an unsigned int representing the position of an stylesheet.cssRules to insert at,
    ...where index-0 is first rule, and index-max is just after last rule and is the same as length of the stylesheet.cssRules in spreadsheet,.

Note: index is now formally required, and omitting it may cause a warning or error. For example:

  • Chrome: " [Warning-icon]  Calling CSSStyleSheet.insertRule() with one argument is deprecated. Please pass the index argument as well"

Return value

The index within the style sheet's rule-list of the newly inserted rule.


CSS stylesheet rule-lists have a number of intuitive and not-so-intuitive restrictions affecting how and where rules can be inserted. Violating these will likely cause an error raised as a DOMException 

  • If index > number of rules in the stylesheet (the CSSRuleList.length), then aborts with IndexSizeError.
  • If rule cannot be inserted at index 0 due to some CSS constraint, then aborts with HierarchyRequestError.
  • If more than one rule is given in the rule parameter, then aborts with SyntaxError
  • If trying to insert an @import at-rule after a style rule, then aborts with HierarchyRequestError.
  • If rule is @namespace at-rule and list has more than just @import at-rules and/or @namespace at-rules, then aborts with InvalidStateError.


Example 1

// push a new rule onto the top of my stylesheet
myStyle.insertRule("#blanc { color: white }", 0); 

Example 2

 * Add a stylesheet rule to the document (may be better practice, however,
 * to dynamically change classes, so style information can be kept in
 * genuine stylesheets (and avoid adding extra elements to the DOM))
 * Note that an array is needed for declarations and rules since ECMAScript does
 * not afford a predictable object iteration order and since CSS is 
 * order-dependent (i.e., it is cascading); those without need of
 * cascading rules could build a more accessor-friendly object-based API.
 * @param {Array} rules Accepts an array of JSON-encoded declarations
 * @example
  ['h2', // Also accepts a second argument as an array of arrays instead
    ['color', 'red'],
    ['background-color', 'green', true] // 'true' for !important rules 
    ['background-color', 'yellow']
function addStylesheetRules (rules) {
  var styleEl = document.createElement('style'),

  // Append style element to head

  // Grab style sheet
  styleSheet = styleEl.sheet;

  for (var i = 0, rl = rules.length; i < rl; i++) {
    var j = 1, rule = rules[i], selector = rules[i][0], propStr = '';
    // If the second argument of a rule is an array of arrays, correct our variables.
    if (Object.prototype.toString.call(rule[1][0]) === '[object Array]') {
      rule = rule[1];
      j = 0;

    for (var pl = rule.length; j < pl; j++) {
      var prop = rule[j];
      propStr += prop[0] + ':' + prop[1] + (prop[2] ? ' !important' : '') + ';\n';

    // Insert CSS Rule
    styleSheet.insertRule(selector + '{' + propStr + '}', styleSheet.cssRules.length);


Specification Status Comment
CSS Object Model (CSSOM)
The definition of 'CSSStyleSheet.insertRule' in that specification.
Working Draft No change from Document Object Model (DOM) Level 2 Style Specification.
Document Object Model (DOM) Level 2 Style Specification
The definition of 'CSSStyleSheet.insertRule' in that specification.
Recommendation Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) 9 (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

Legacy browser support

  • Internet Explorer - pre v9

    addRule(selector, rule [, index]);  --  Example: addRule('pre', 'font: 14px verdana'); // add rule at end

    Also note the non-standard removeRule() and .rules instead of deleteRule() and .cssRules respectively.

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API CSSOM CSSStyleSheet Method NeedsBrowserCompatibility NeedsMarkupWork NeedsMobileBrowserCompatibility Reference