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<script type="text/javascript"> var originalOnError = window.onerror; function setupRunner(name, fn) { var testRunner = document.querySelector('[data-run='+name+']'); var testOutput = document.querySelector('[data-output='+name+']'); testRunner.addEventListener('click', function () { window.onerror = function(message, source, lineno, colno, error) { var stack = error && error.stack; var onerror = JSON.stringify({ message: message, source: source, lineno: lineno, colno: colno }, null, 2); var errObj = JSON.stringify({ message: error && error.message, sourceURL: error && error.sourceURL, line: error && error.line, column: error && error.column }, null, 2); testOutput.innerHTML = '=== Stack ===
' + stack + '

=== window.onerror args ===
' + onerror + '

=== window.onerror error arg ===
' + errObj; return true; }; fn(); window.onerror = originalOnError; }); } </script>

Errors which are not caught in a try/catch will bubble up the window's error handler. This is your last chance to log the error for reporting. Some browsers report slightly different information, or will not report any information at all. This page will interactively explain these intricacies, and acts as a "test runner".

Inline function on same page

This function is inlined into this page, so it is served from the same domain. Error reporting should be correct.

function inlineFn () {
  throw new Error('inlineFn-error');
}

Run inlineFn()

<script type="text/javascript"> function inlineFn () { throw new Error('inline-error'); } setupRunner("inlineFn", inlineFn); </script>

Browser	window.onerror msg	window.onerror url	window.onerror line:col	error msg	error url	error line:col
Chrome	Uncaught Error: inline-error	https://safari-cors-errors.framba.ch/	79:3	inline-error
Firefox	Error: inline-error	https://safari-cors-errors.framba.ch/	79:9	inline-error
Safari	Error: inline-error	https://safari-cors-errors.framba.ch/	79:34	inline-error	https://safari-cors-errors.framba.ch/	79:18

Generated function on same page

An inline script generates a new function from a string and executes it.

function newFn () {
  var fn = new Function("throw new Error('newFn-error')");
  fn();
}

Run newFn()

<script type="text/javascript"> function newFn () { var fn = new Function("throw new Error('newFn-error')"); fn(); } setupRunner("newFn", newFn); </script>

| Browser | window.onerror
msg | window.onerror
url | window.onerror
line:col | error
msg | error
url
line:col | |:------|:------|:------|:------|:------|:------|:------| | Chrome | Uncaught Error: newFn-error | https://safari-cors-errors.framba.ch/ | 3:1 | newFn-error | | | Firefox | Error: newFn-error | https://safari-cors-errors.framba.ch/ line 143 > Function | 3:7 | newFn-error | | | Safari | Error: newFn-error | | 2:16 | newFn-error | | 2:16 |

Calling an external function

This function is defined on a different domain, with crossorigin="anonymous" and CORS enabled. Safari shows "Script Error.", ostensibly for secrity reasons.

// Defined externally
function externalFn() {
  throw new Error("externalFn-error");
}

Run externalFn()

<script type="text/javascript"> setupRunner("externalFn", externalFn); </script>

| Browser | window.onerror
msg | window.onerror
url | window.onerror
line:col | error
msg | error
url
line:col | |:------|:------|:------|:------|:------|:------|:------| | Chrome | Uncaught Error: external-cors-error | https://safari-cors-external.framba.ch/external-fn.js | 2:9 | external-cors-error | | | Firefox | Error: external-cors-error | https://safari-cors-external.framba.ch/external-fn.js | 2:9 | external-cors-error | | | Safari | Script error. | | | | | |

Calling and rethrowing an external function

This function is defined on a different domain, with crossorigin="anonymous" and CORS enabled. On our domain, we try/catch the function call, but immediately rethrow the error.

// Defined externally
function externalFn() {
  throw new Error("external-cors-error");
}

// Defined inline
function rethrowExternalFn() {
  try {
    externalFn();
  } catch (e) {
    throw e;
  }
}

Run rethrowExternalFn()

<script type="text/javascript"> function rethrowExternalFn() { try { externalFn(); } catch (e) { throw e; } } setupRunner("rethrowExternalFn", rethrowExternalFn); </script>

| Browser | window.onerror
msg | window.onerror
url | window.onerror
line:col | error
msg | error
url
line:col | |:------|:------|:------|:------|:------|:------|:------| | Chrome | Uncaught Error: external-cors-error | https://safari-cors-errors.framba.ch/ | 283:5 | external-cors-error | | | Firefox | Error: external-cors-error | https://safari-cors-external.framba.ch/external-fn.js | 2:9 | external-cors-error | | | Safari | Error: external-cors-error | https://safari-cors-errors.framba.ch/ | 283:12 | external-cors-error | https://safari-cors-external.framba.ch/external-fn.js | 2:18 |