Automatically add ALT from Image file name

AddALTtagFromImageName.js

jQuery( document ).ready(function() {
    String.prototype.filename=function(extension){
        var s= this.replace(/\\/g, '/');
        s= s.substring(s.lastIndexOf('/')+ 1);
        return extension? s.replace(/[?#].+$/, ''): s.split('.')[0];
    }
    jQuery("img").each(function () { 
        var alt = jQuery(this).attr('alt');
        if(alt === ""){
            var namefile = jQuery(this).attr('src').filename();
            var rep = namefile.replace(/[_#?%*$@!=&]/g,'-');
            var temp = rep.split('-');
            var alt ='';
            for (i = 0; i < temp.length; i++) { 
              alt =  alt+' '+temp[i];
            }
            jQuery(this).attr('alt',alt);
        }
		if(alt === undefined){
            var namefile = jQuery(this).attr('src').filename();
            var rep = namefile.replace(/[_#?%*$@!=]/g,'-');
            var temp = rep.split('-');
            var alt ='';
            for (i = 0; i < temp.length; i++) { 
              alt =  alt+' '+temp[i];
            }
            jQuery(this).attr('alt',alt);
        }
    });
});