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Syntactically-aware grep for JavaScript
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bin This adds support for applying overlapping patches to the same AST wi…
lib Merge pull request #4 from oyvindkinsey/patch2
narcissus @ 835c141 Fix patcher for multiple source modifications
specs Added support of "with "statement.
tests Support if in patterns
.gitmodules Switch to submodule for narcissus
LICENSE License headers
README.mdown Update README.mdown
package.json Fix output bug for jsgrep


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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