Low footprint ECMAScript source code parser


Low footprint, fast source code parser, which allows you to find all code fragment occurrences with respect to all syntax rules that cannot be handled with plain regular expression search.

It aims at use cases where we need to quickly find usage of given function, property etc. in syntactically valid code.

$ npm install esniff

To port it to Browser or any other (non CJS) environment, use your favorite CJS bundler. No favorite yet? Try: Browserify, Webmake or Webpack

Using main module you can configure sophisticated parser on your own. However, first, see preprared API utilities that may already address use cases you have.

  • code Code to parse
  • triggerChar Character which is expected to trigger custom handling via callback
  • callback To detect and eventually handle case we're after

Example: Find all require(..) calls:

var esniff = require('esniff');
var result = esniff('var x = require(\'foo/bar\')', 'r', function (indexpreviousnest) {
  if (previous === '.') return next(); // Ignore x.require calls 
  if (code.indexOf('require', index) !== index) return; // Not really `require` call 
  next('require'.length); // Move after `require` and skip any following whitespace 
  index = esniff.index; // Update index 
  if (code[i] !== '(') return resume(); // Not `require(` 
  return collectNest(); // Collect all code between parenthesis 
console.log(result);  [{ point: 17, column: 17, line: 1, raw: '\'foo/bar\'' }]

Returns function which allows us to find all accessed property names on given object name

var findProperties = require('esniff/accessed-properties');
var findContextProperties = findProperties('this');
var result = findContextProperties('var foo = "0"; = foo; this.someMethod(); otherFunction()');
console.log(result); // [ { name: 'bar', start: 20, end: 23 }, { name: 'someMethod', start: 36, end: 46 } ] 

Returns function which allows us to find all occurrences of given function (or method) being invoked

Through options we can restrict cases which we're after:

  • asProperty (default: false), on true will allow when we search for name calls
  • asPlain (default: true), on true it allows plain calls e.g. name() when we search for name. Should be set to false if we're strictly about method calls.

Setting both asProperty and asPlain to false, will always produce empty result

var findRequires = require('esniff/function')('require');
findRequires('var x = require(\'foo/bar\')');
// [{ point: 17, column: 17, line: 1, raw: '\'foo/bar\'' }] 

Resolves expressions separated with commas, with additional limit you can specify after which number of arguments resolver should stop

var resolveArgs = require('esniff/resolve-arguments');
var result = resolveArgs('"raz", "dwa", [\'raz\'\'dwa\'], "trzy"', 3));
console.log(result); // ['"raz"', ' "dwa"', ' [\'raz\', \'dwa\']'] 
  • esniff assumes code that you pass is syntactically correct, it won't inform you about any syntax errors and may produce unexpected and nonsense results when such code is used.
  • There's single case of syntactically correct code, which will make esniff produce incorrect results, it's division made directly on object literal (e.g. x = { foo: 'bar' } / 14, esniff in that case will assume that / starts regular expression). Still there's not known use case where such code may make any sense, and many popular JS source code parsers share very same vulnerability.
  • esniff may work with new syntax introduced by ECMAScript 6 but it has not been fully revised in that matter yet. Pull requests are welcome.


$ npm test