MediaWiki:Gadget-DetectDir.js

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// This is the function that does all the hard work.
// Just pass a form element element (or array of form elements) to the 
// i18n.addElements method.

// The idea and regular expressions originally located within the goog.i18n.bidi 
// Javascript library (http://code.google.com/apis/gadgets/docs/i18n.html) and I
// take no credit what-so-ever for the idea.

var i18n = (function i18n() {           
        var ltrChars            = 'A-Za-z\u00C0-\u00D6\u00D8-\u00F6\u00F8-\u02B8\u0300-\u0590\u0800-\u1FFF'+'\u2C00-\uFB1C\uFDFE-\uFE6F\uFEFD-\uFFFF',
            rtlChars            = '\u0591-\u07FF\uFB1D-\uFDFD\uFE70-\uFEFC',
            ltrDirCheckRe       = new RegExp('^[^'+rtlChars+']*['+ltrChars+']'),
            rtlDirCheckRe       = new RegExp('^[^'+ltrChars+']*['+rtlChars+']');

        // Inbuilt addEvent function
        function addEvent(obj, type, fn, tmp) {
                tmp || (tmp = true);
                if( obj.attachEvent ) {
                        obj["e"+type+fn] = fn;
                        obj[type+fn] = function(){obj["e"+type+fn]( window.event );};
                        obj.attachEvent( "on"+type, obj[type+fn] );
                } else {
                        obj.addEventListener( type, fn, true );
                };
        };
        
        function addElemEvents(elem) {                 
                addEvent(elem, "keydown", check);
                addEvent(elem, "keyup",   check);
                checkDirection(elem);
        };
        
        function check(e) {
                checkDirection(this);
        };
        
        function checkDirection(elem) {
                var text = elem.value;                 
                elem.dir = isRtlText(text) ? 'rtl' : (isLtrText(text) ? 'ltr' : '');    
        };
        
        function isRtlText(text) {
                return rtlDirCheckRe.test(text);
        };
        
        function isLtrText(text) {
                return ltrDirCheckRe.test(text);
        };
        
        return {
                addElements: function(elems) {
                        if(!elems.length) elems = [elems];
                        for(var i = 0, elem; elem = elems[i]; i++) {                                  
                                addElemEvents(elem);                                  
                        };
                }
        };
})();

window.onload = function(e) {
        i18n.addElements([document.getElementById('wpTextbox1'), document.getElementById('searchInput')]);
};