security error the operation is insecure in firefox document.stylesheets
error-handling, javascript, security, stylesheet
Solution
To circumvent the SecurityError in Firefox when attempting to access the cssRules attribute, you must use a `try/catch` statement. The following should work:
// Example call to process_stylesheet() with StyleSheet object.
process_stylesheet(window.document.styleSheets[0]);
function process_stylesheet(ss) {
// cssRules respects same-origin policy, as per
// https://code.google.com/p/chromium/issues/detail?id=49001#c10.
try {
// In Chrome, if stylesheet originates from a different domain,
// ss.cssRules simply won't exist. I believe the same is true for IE, but
// I haven't tested it.
//
// In Firefox, if stylesheet originates from a different domain, trying
// to access ss.cssRules will throw a SecurityError. Hence, we must use
// try/catch to detect this condition in Firefox.
if(!ss.cssRules)
return;
} catch(e) {
// Rethrow exception if it's not a SecurityError. Note that SecurityError
// exception is specific to Firefox.
if(e.name !== 'SecurityError')
throw e;
return;
}
// ss.cssRules is available, so proceed with desired operations.
for(var i = 0; i < ss.cssRules.length; i++) {
var rule = ss.cssRules[i];
// Do something with rule
}
}
Problem
The following code throws an error in the Firefox Console at the line with the continue. ``` SecurityError: The operation is insecure. if( !sheet.cssRules ) { continue; } ``` However does not in Chrome and IE 11... Can someone explain the -why- of this? (And also how to re-work to make it safe.) I assume this is a cross-domain issue, but I'm stuck as how to re-work the code properly. ``` var bgColor = getStyleRuleValue('background-color', 'bg_selector'); function getStyleRuleValue(style, selector, sheet) { var sheets = typeof sheet !== 'undefined' ? [sheet] : document.styleSheets; for (var i = 0, l = sheets.length; i < l; i++) { var sheet = sheets[i]; if( !sheet.cssRules ) { continue; } for (var j = 0, k = sheet.cssRules.length; j < k; j++) { var rule = sheet.cssRules[j]; if (rule.selectorText && rule.selectorText.split(',').indexOf(selector) !== -1) return rule.style[style]; } } return null; } ```