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JavaScript warnings are generated when code is executed that doesn't cause a run-time error, but is non-standard, poorly written, or prone to cause logic errors. This preference controls whether JavaScript warnings are logged to the JavaScript Console.

Possible values and their effects


Show JavaScript errors and warnings.


Show JavaScript errors only. (Default)


Mozilla Suite

Edit→Preferences→Debug→Show strict JavaScript warnings

Recommended settings

Web developers, extension developers, and hackers should have this preference set to true.

First checked in

1999-11-11 by Brendan Eich.

Has an effect in

  • Netscape (all versions since 6.0)
  • Mozilla Suite (all versions since M11)
  • Phoenix (all versions)
  • Firebird (all versions)
  • Firefox (all versions)
  • Thunderbird (all versions)
  • Calendar (all versions)
  • Minimo (all versions)
  • SeaMonkey (all versions)

Related preferences

See also

External links