jq.mobi.js

{
        removeClass: function (name) {
            for (var i = 0; i < this.length; i++) {
                if (name === undefined) { this[i].className = ''; return this; }
                var classList = this[i].className;
                name.split(/\s+/g).forEach(function (cname) {
                    classList = classList.replace(classRE(cname), "");
                });
                if (classList.length > 0)
                    this[i].className = classList.trim();
                else
                    classList = "";
            }
            return this;
        }
}

zepto.js

{
    removeClass: function(name){
      return this.each(function(idx) {
        if(name === undefined)
          return this.className = '';
        classList = this.className;
        funcArg(this, name, idx, classList).split(/\s+/g).forEach(function(klass) {
          classList = classList.replace(classRE(klass), " ")
        });
        this.className = classList.trim()
      });
    }
}