faster AC filtering.js

YAHOO.widget.AutoComplete.prototype.filterResults =
function( filter, response, parsedResponse, callback ) {
    // If AC has passed a filter string value back to itself, grab it
    if ( callback && callback.argument && callback.argument.query ) {
        filter = callback.argument.filter;
    }           
    filter = decodeURIComponent( filter ).toLowerCase();
    
    // Only if a filter string is available to match against
    if ( filter ) {
            
        var results  = parsedResponse.results,
            filtered = [],
            limit    = callback.scope.maxResultsDisplayed,
            fields   = this.responseSchema.fields,
            key      = ( fields ? fields[0].key || fields[0] : null ),
            lang     = YAHOO.lang,
            isString = lang.isString,
            isArray  = lang.isArray,
            matched  = 0,
            i, len, result;

        for( i = 0, len = results.length; i < len; ++i ) {
            result = results[i];

            if ( !isString( result ) ) {
                if ( isArray( result ) ) {
                    result = result[0];
                } else if ( key ) {
                    result = result[ key ];
                } else if ( this.key ) {
                    result = result[ this.key ];
                } else {
                    result = '';
                }    
            }
            
            if ( result.toLowerCase().indexOf( filter ) > -1 ) {
                matched = filtered.push( results[i] );
            }

            // Filter no more if maxResultsDisplayed is reached
            if ( matched >= limit ) {
                break;
            }
        }   
                
        parsedResponse.results = filtered;
    }           
                    
    return parsedResponse;
};