strip-accents.js

function stripAccents(str) {
    var reAccents = /[àáâãäçèéêëìíîïñòóôõöùúûüýÿÀÁÂÃÄÇÈÉÊËÌÍÎÏÑÒÓÔÕÖÙÚÛÜÝ]/g;
    var replacements = 'aaaaaceeeeiiiinooooouuuuyyAAAAACEEEEIIIINOOOOOUUUUY';
    return str.replace(reAccents, function (match) {
        return replacements[reAccents.source.indexOf(match)];
    });
};

stripAccents('àá');
// aa

Just a heads up, this has an off-by-one bug:
reAccents.source is

"[àáâãäçèéêëìíîïñòóôõöùúûüýÿÀÁÂÃÄÇÈÉÊËÌÍÎÏÑÒÓÔÕÖÙÚÛÜÝ]"

So:

stripAccents('àáâãäçèéêëìíîïñòóôõöùúûüýÿÀÁÂÃÄÇÈÉÊËÌÍÎÏÑÒÓÔÕÖÙÚÛÜÝ')
// aaaaceeeeiiiinooooouuuuyyAAAAACEEEEIIIINOOOOOUUUUYundefined'

Simple/hacky fix: add a dummy character prefix to replacements:

function stripAccents(str) {
    var reAccents = /[àáâãäçèéêëìíîïñòóôõöùúûüýÿÀÁÂÃÄÇÈÉÊËÌÍÎÏÑÒÓÔÕÖÙÚÛÜÝ]/g;

    // Prefixed with some char to avoid off-by-one:
    var replacements = '_aaaaaceeeeiiiinooooouuuuyyAAAAACEEEEIIIINOOOOOUUUUY';

    return str.replace(reAccents, function (match) {
        return replacements[reAccents.source.indexOf(match)];
    });
};

stripAccents('àáâãäçèéêëìíîïñòóôõöùúûüýÿÀÁÂÃÄÇÈÉÊËÌÍÎÏÑÒÓÔÕÖÙÚÛÜÝ')
// 'aaaaaceeeeiiiinooooouuuuyyAAAAACEEEEIIIINOOOOOUUUUY'