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CSSStyleSheet.insertRule

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

Note: Although insertRule() is exclusively a method of CSSStyleSheet, it actually inserts the rule into CSSStyleSheet.cssRules — its internal CSSRuleList.

Syntax

stylesheet.insertRule(rule[, index])

Parameters

rule

A DOMString containing the rule to be inserted. What the inserted rule must contain depends on its type:

For rule-sets, both a selector and a style declaration.
For at-rules, both an at-identifier and the rule content.

index Optional

A positive integer less than or equal to stylesheet.cssRules.length, representing the newly inserted rule's position in CSSStyleSheet.cssRules. The default is 0. (In older implementations, this was required. See Browser Compatibility for details.)

Return value

The newly inserted rule's index within the stylesheet's rule-list.

Restrictions

CSS has intuitive and not-so-intuitive restrictions affecting where rules can be inserted. Violating them will likely raise a DOMException .

If index > 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 and the rule-list has more than just @import at-rules and/or @namespace at-rules, then aborts with InvalidStateError.

Examples

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 (it may be better practice
 * 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 guarantee a predictable object iteration order, and since CSS is 
 * order-dependent.
 * @param {Array} rules Accepts an array of JSON-encoded declarations
 * @example
addStylesheetRules([
  ['h2', // Also accepts a second argument as an array of arrays instead
    ['color', 'red'],
    ['background-color', 'green', true] // 'true' for !important rules 
  ], 
  ['.myClass', 
    ['background-color', 'yellow']
  ]
]);
*/
function addStylesheetRules (rules) {
  var styleEl = document.createElement('style');

  // Append <style> element to <head>
  document.head.appendChild(styleEl);

  // Grab style element's sheet
  var styleSheet = styleEl.sheet;

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

Specifications

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.	Obsolete	Initial definition

Polyfill

The below polyfill will correct the input of the arguments of insertRule to standardize them in Internet Explorer 5–8. It supplements insertRule with a function that separates the selector from the rules before sending the arguments to the default native insertRule.

(function(Sheet_proto){
    var originalInsertRule = Sheet_proto.insertRule;
    if (originalInsertRule.length === 2){ // 2 mandatory arguments: (selector, rules)
        Sheet_proto.insertRule = function(selectorAndRule){
            // First, separate the selector from the rule
            a: for (var i=0, Len=selectorAndRule.length, isEscaped=0, newCharCode=0; i !== Len; ++i) {
                newCharCode = selectorAndRule.charCodeAt(i);
                if (!isEscaped && (newCharCode === 123)) { // 123 = "{".charCodeAt(0)
                    // Secondly, find the last closing bracket
                    var openBracketPos = i, closeBracketPos = -1;
                    for (; i !== Len; ++i) {
                        newCharCode = selectorAndRule.charCodeAt(i);
                        if (!isEscaped && (newCharCode === 125)) { // 125 = "}".charCodeAt(0)
                            closeBracketPos = i;
                        }
                        isEscaped ^= newCharCode===92?1:isEscaped; // 92 = "\\".charCodeAt(0)
                    }
                    if (closeBracketPos === -1) break a; // no closing bracket was found!
                    /*else*/ return originalInsertRule.call(
                        this, // the sheet to be changed
                        selectorAndRule.substring(0, openBracketPos), // the selector
                        selectorAndRule.substring(closeBracketPos), // the rule
                        arguments[3] // the insert index
                    );
                }
                // works by if the char code is a backslash, then isEscaped gets flipped (XOR-ed by
                // 1), and if it is not a backslash then isEscaped gets XORed by itself, zeroing it
                isEscaped ^= newCharCode===92?1:isEscaped; // 92 = "\\".charCodeAt(0)
            }
            // Else, there is no unescaped bracket
            return originalInsertRule.call(this, selectorAndRule, "", arguments[2]);
        };
    }
})(CSSStyleSheet.prototype);

Browser compatibilityUpdate compatibility data on GitHub

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	Yes	Yes	Yes	9	Yes	Yes
`index` is optional	60	?	?	?	47	?

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	Yes	Yes	Yes	Yes	Yes	Yes	?
`index` is optional	60	60	?	?	47	?	?

Legacy browser support

Internet Explorer 8 and below

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.