The average identifier length in popular JavaScript libraries is 8.27 characters.

Identifiers longer than 15 are less common than single characters. The most common are 6-character names. Such results were obtained by Esprima, a parser for JavaScript written in JavaScript , after analyzing the source code of libraries such as jQuery, Prototype, MooTools, Underscore, and some others.

The five longest identifiers look like this:

prototype-1.7.0.0.js	SCRIPT_ELEMENT_REJECTS_TEXTNODE_APPENDING
prototype-1.7.0.0.js	MOUSEENTER_MOUSELEAVE_EVENTS_SUPPORTED
jquery-1.7.1.js	subtractsBorderForOverflowNotVisible
jquery.mobile-1.0.js	getClosestElementWithVirtualBinding
prototype-1.7.0.0.js	HAS_EXTENDED_CREATE_ELEMENT_SYNTAX

With the help of such a script for Node.js, you can compare your style of naming variables and functions with classical samples for excessive verbosity or too harsh brevity:

 var fs = require('fs'), esprima = require('esprima'), files = process.argv.splice(2); files.forEach(function (filename) { var identifiers = {}, content = fs.readFileSync(filename, 'utf-8'), syntax = esprima.parse(content); JSON.stringify(syntax, function (key, value) { if (key === 'name' && typeof identifiers[value] === 'undefined') { identifiers[value] = value.length; } return value; }); for (var key in identifiers) { if (identifiers.hasOwnProperty(key)) { console.log(identifiers[key]); } } }); 

Run like this:
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 node idlen.js /path/to/some/*.js | sort -n | uniq -c