jQuery.fn.extend({
    removeClass: function( value ) {
        var classes, elem, cur, clazz, j, finalValue,
            i = 0,
            len = this.length,
            proceed = arguments.length === 0 || typeof value === "string" && value;
        if ( jQuery.isFunction( value ) ) {
            return this.each(function( j ) {
//这里就是根据你传递的移除类名的函数返回的类名，再次调用removeClass自身了。
                jQuery( this ).removeClass( value.call( this, j, this.className ) );
            });
        }
        if ( proceed ) {
            classes = ( value || "" ).match( rnotwhite ) || [];
            for ( ; i < len; i++ ) {
                elem = this[ i ];
                cur = elem.nodeType === 1 && ( elem.className ?
                    ( " " + elem.className + " " ).replace( rclass, " " ) :
                    ""
                );
                if ( cur ) {
                    j = 0;
                    while ( (clazz = classes[j++]) ) {
//区别在下面的while循环，当检索到当前DOM元素包含你要移除的类名，会用replace替换成" "
                        while ( cur.indexOf( " " + clazz + " " ) >= 0 ) {
                            cur = cur.replace( " " + clazz + " ", " " );
                        }
                    }
//下面也是关键区别之一，判断你是否传递了要移除的类名value。如果没有传递，则finalValue=""，如果此时DOM元素有类名的话，也就是条件为true，移除DOM元素的所有类名；
//如果传递了，则移除匹配的类名，移除后，没有移除的类名拼接成了cur，去掉左右两端的空格字符串，将DOM元素的类名设置成cur。
                    finalValue = value ? jQuery.trim( cur ) : "";
                    if ( elem.className !== finalValue ) {
                        elem.className = finalValue;
                    }
                }
            }
        }
        return this;
    }
});