A JavaScript port of the Apache Lucene ASCII Folding Filter that converts alphabetic, numeric, and symbolic Unicode characters which are not in the first 127 ASCII characters (the "Basic Latin" Unicode block) into their ASCII equivalents, if one exists.

Npm: npm install fold-to-ascii

Bower: bower install fold-to-ascii

This version no longer exposes the window.foldToAscii variable in favour of a more modular approach using npm's module.exports. Should you require a stand-alone version, Browserify appears to be the tool of choice (browserify index.js > bundle.js).

It is simple:

var foldToAscii = require("fold-to-ascii");

// Folding with replacement of unmapped characters with the "_" character:
console.log(foldToAscii.fold("★Lorém ïpsum dölor.", "_"));
// Results in "_Lorem ipsum dolor."

// Folding without replacement of unmapped characters:
console.log(foldToAscii.fold("★Lorém ïpsum dölor.", null));
console.log(foldToAscii.fold("★Lorém ïpsum dölor."));
// Both calls result in "Lorem ipsum dolor."

If no replacement parameter is specified, unmapped characters will be replaced by the empty string.

All replacement tasks are covered by QUnit tests. Run npm test.

This is a straightforward port of the very extensive switch/case statement found in http://svn.apache.org/repos/asf/lucene/java/tags/lucene_solr_4_5_1/lucene/analysis/common/src/java/org/apache/lucene/analysis/miscellaneous/ASCIIFoldingFilter.java

The function to determine character codes is taken from a code example in the MDN (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/charCodeAt#Example.3A_Fixing_charCodeAt_to_handle_non-Basic-Multilingual-Plane_characters_if_their_presence_earlier_in_the_string_is_unknown).

The unambiguous allocation of characters to replacements is not possible since it is language-dependent. For example a user from France might expect ü to be replaced with u while a user from Germany expects the replacement to be ue.