Javascript.options.relimit

From MozillaZine Knowledge Base

The title given to this article is incorrect due to technical limitations. The correct title is javascript.options.relimit.

This article describes the preference javascript.options.relimit. To add, delete, or modify this preference, you will need to edit your configuration — do not edit this article.

1 Background
2 Possible values and their effects
- 2.1 True
- 2.2 False
3 Caveats
4 First checked in
5 Has an effect in
6 Related bugs
7 Related preferences

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Background

Some regular expressions can, based on the length of the text processed, take exponential amounts of time to run. As Mozilla’s JavaScript engine implements regular expressions, it is possible to hang a browser or other Mozilla application using one of these “exponentially explosive” regular expressions.

To guard against this possibility, checks are performed internally to catch these regular expressions before they consume too much processing time. This preference determines whether problematic regular expressions should throw an exception, stopping execution.

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Possible values and their effects

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True

Throw an exception when a regular expression backtracks more than n³ times, where n is the length of the input string.

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False

Ignore large amounts of backtracking in regular expressions. (Default)

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Caveats

Setting this preference to true may cause perfectly valid JavaScript to break if included regular expressions are too complex.
Mozilla applications may become unresponsive on certain regular expressions if this preference is set to false.

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