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Syntactically-aware grep for JavaScript
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jsgrep: a syntactically-aware grep for 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.


Find calls to window.setTimeout with a 0 timeout

$ jsgrep 'setTimeout(A, 0)' tests/*.js
tests/jquery.js:        setTimeout( function() {
tests/jquery.js:    setTimeout( clearFxNow, 0 );

Jsgrep uses metavariables as wildcards. Metavariables match any valid JavaScript chunk, so in this case, the first match was an entire inline function. In both cases, the second parameter to setTimeout was a literal value of 0.

Find value defaulting

$ jsgrep "A = A || B;" tests/*.js
tests/jquery.js:            args = args || [];
tests/jquery.js:    dataType = dataType || options.dataTypes[ 0 ];

When the pattern references the same metavariable multiple times, jsgrep ensures that the value of the metavariable is the same throughout the match.

Find the names of all invoked events

$ ./jsgrep -p B ", ...)" tests/*.j
tests/connect.js: 'auth.logout'
tests/connect.js: 'auth.login'

The ... operator matches 0 or more expressions in function calls and array initializers.

Find 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 you to search object initializations partially, which enables easily drilling into the structure of JavaScript classes. This example also uses the -p flag to print only a particular matched variable.


  • Consider a metavar that matches but doesn't save, to prevent ambiguities.
  • Consider support for --where/--eval and/or not-patterns
  • Support for most statements in patterns
  • 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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