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 ) {
//這里就是根據你傳遞的移除類名的函數返回的類名，再次調用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++]) ) {
//區別在下面的while循環，當檢索到當前DOM元素包含你要移除的類名，會用replace替換成" "
                        while ( cur.indexOf( " " + clazz + " " ) >= 0 ) {
                            cur = cur.replace( " " + clazz + " ", " " );
                        }
                    }
//下面也是關鍵區別之一，判斷你是否傳遞了要移除的類名value。如果沒有傳遞，則finalValue=""，如果此時DOM元素有類名的話，也就是條件為true，移除DOM元素的所有類名；
//如果傳遞了，則移除匹配的類名，移除后，沒有移除的類名拼接成了cur，去掉左右兩端的空格字符串，將DOM元素的類名設置成cur。
                    finalValue = value ? jQuery.trim( cur ) : "";
                    if ( elem.className !== finalValue ) {
                        elem.className = finalValue;
                    }
                }
            }
        }
        return this;
    }
});