FindProxyForURL Beta

PAC-E018 · console-in-pac

console.log or other browser APIs used in the PAC

high · Errors and robustness

The PAC sandbox is not a web page. console, window, document, fetch, setTimeout and similar objects are not defined; using them throws a ReferenceError and aborts the evaluation.

Why it matters

PAC code runs in a minimal JavaScript context that provides the PAC helpers and the ECMAScript built-ins only. console.log(host) left over from debugging in a browser’s developer console throws ReferenceError: console is not defined when the engine runs it, which has the same effect as any other exception (PAC-E006): the request is handled as a script failure. The only debugging output function defined by the PAC specification is alert(), whose behaviour also varies (PAC-K002).

Draft until the exact set of undefined globals per engine has been confirmed in the lab; Chromium’s resolver context is defined by its PAC JavaScript library plus V8 built-ins.

How to fix

Remove console/window/document references; use a test harness outside the PAC for debugging.

Examples

Bad

function FindProxyForURL(url, host) {
  console.log("PAC called for " + host);
  return "PROXY proxy.corp.example:8080";
}
Open bad example in checker

Good

function FindProxyForURL(url, host) {
  return "PROXY proxy.corp.example:8080";
}
Open good example in checker

Engine behaviour

EngineBehaviourSource
chromiumResolver context provides only the PAC helpers and ECMAScript built-ins; console is not defined.expert, unverified

Source: code = read in the engine's source, doc = vendor documentation, lab = observed in a lab run, expert = practitioner knowledge, not yet verified.

Related rules

References