Limited support Avoid in modern code. Prefer constructing a fresh regular expression with explicit inputs.

RegExp compile()

Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

Note: The compile() method is only specified for compatibility reasons. Using compile() causes the otherwise immutable regex source and flags to become mutable, which may break user expectations. You can use the RegExp() constructor to construct a new regular expression object instead.

The compile() method of RegExp instances is used to recompile a regular expression with new source and flags after the RegExp object has already been created.

RegExpLegacyDeprecated

Browser support

Feature Desktop Mobile
Chrome
Edge
Firefox
Safari
Chrome Android
Safari iOS
javascript.builtins.RegExp.compile
Deprecated
1
12
1
3.1
18
2
1+Supported (version) Not supported ※Has note Sub-feature descriptions sourced from MDN Web Docs (CC BY-SA 2.5)

Syntax

JAVASCRIPT 
// RegExp compile() example
// See MDN Web Docs for details

Live demo

Reuse one RegExp object

Call compile when available to replace the pattern on the same instance.

JavaScript
Output
Press the Run button

Switch between patterns

Retarget a single RegExp instance to check multiple formats.

JavaScript
Output
Press the Run button

Compare with new RegExp

Show the modern alternative to compile by constructing a new RegExp.

JavaScript
Output
Press the Run button

Use cases

  • Regex modernization

    Replace compile()-based flows with clearer new RegExp(...) creation during refactors.

  • Legacy code reading

    Recognize what compile is doing when auditing historical regular-expression utilities.

Cautions

  • Mutating regex objects makes pattern flow harder to follow than building a fresh value.
  • Deprecated APIs increase maintenance cost and rarely justify their continued use.

Accessibility

  • No direct accessibility effect, but clearer validation code supports more reliable user feedback.
  • Prefer maintainable regex handling in forms and parsing paths that drive visible errors.

Related links