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;     } });