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Syntactically-aware grep for JavaScript
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Archived Repo

This is an archived project and is no longer supported or updated by Facebook. Please do not file issues or pull-requests against this repo. If you wish to continue to develop this code yourself, we recommend you fork it.

Proceed and be bold!

jsgrep / jspatch - toolkit for searching and modifying JavaScript

Jsgrep is program that searches for a particular JavaScript pattern using the abstract syntax tree (AST) of the program. This enables matching expressions based on their JavaScript meaning, rather than based on simple strings. Jspatch is a tool to take that information and programmatically modify the original source code.


Jsgrep: find Javelin classes that have a 'path' property

$ jsgrep -p C "JX.install(C, { properties: { path: X } })" tests/*.js
tests/javelin.js: 'Event'
tests/javelin.js: 'URI'

Jsgrep allows easily drilling into the structure of JavaScript classes. In this example, jsgrep finds Javelin classes that contain a 'path' property. The class name is stored in the metavariable C, which will be output.

Jspatch: replace setTimeout with window.setTimeout in jQuery

$ jspatch -e 's/setTimeout( A, B )/window.setTimeout( A, B )/' tests/jquery.js
--- tests/jquery.js 2012-01-10 14:51:36.000000000 -0800
+++ /tmp/jspatch.jquery.js  2012-01-11 17:13:56.000000000 -0800
@@ -420,7 +420,7 @@
        if ( (wait === true && !--jQuery.readyWait) || (wait !== true && !jQuery.isReady) ) {
            // Make sure body exists, at least, in case IE gets a little overzealous (ticket #5443).
            if ( !document.body ) {
-               return setTimeout( jQuery.ready, 1 );
+               return window.setTimeout( jQuery.ready, 1 );

            // Remember that the DOM is ready
@@ -1987,7 +1987,7 @@
        ( src === "mark" || !jQuery._data(elem, markDataKey) ) ) {
        // Give room for hard-coded callbacks to fire first
        // and eventually mark/queue something else on the element
-       setTimeout( function() {
+       window.setTimeout( function() {
            if ( !jQuery._data( elem, queueDataKey ) &&
                !jQuery._data( elem, markDataKey ) ) {
                jQuery.removeData( elem, deferDataKey, true );

Jspatch supports a versatile patch file format that can perform far more complex transformations as well. For more information, see the online documentation.


npm install jsgrep-toolkit

To install from source code:

git clone
cd jsgrep
git submodule update --init
npm install


  • Consider a metavar that matches but doesn't save, to prevent ambiguities.
  • Rewrite forEachNode to be iterative rather than recursive (to fix ...)
  • Consider support for --where/--eval and/or not-patterns
  • Support for most statements in patterns
  • Formally testing the pattern matchers


  • Testing


Jsgrep was written by Ryan Patterson at Facebook. Inspiration for this project draws heavily from pfff, a source code analyzer written at Facebook.

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