有没有办法以更优雅，更优化的方式编写这一小段代码？ （ES6）

Question

我一直在尝试自学ES6。这是我学到的一些小例子，比如let，const和=＆gt;功能。是否有更优雅或更短的方式来写这个？也许用forEach替换for循环？欢迎任何提示和帮助。

'use strict';
const countChar = (string, ch) => {
    let counted = 0;
    for (let i = 0; i < string.length; i++) {
        if (string.charAt(i) === ch) {
            counted += 1;
        }
    }
    return counted;
};

const countBs = string => countChar(string, 'B');

console.log(countBs('BBC'));
console.log(countChar('kakkerlak', 'k'));

Answer 1

这是缩短它的另一种方法

SELECT  
    Customerid, CustomerName, [ftga.ihs.com] as ftga, [Email Delivery] as Email 
FROM  
    (SELECT 
         Customerid, CustomerName, AliasName, 
         Deliverylocation,FTPUsername,FTPPassword
     FROM
         [dbo].[tblCustomerDeliveryServerMapping] t1
     INNER JOIN
         tblDeliveryServerDetails t2 ON t1.Deliveryserverid = t2.id
     INNER JOIN
         tblcustomerinfo t3 ON t1.customerid = t3.id) AS P
PIVOT 
    (MAX(Deliverylocation + FTPUsername + FTPPassword) 
     FOR AliasName in ([ftga.ihs.com],[Email Delivery])
    ) AS  PVT

Answer 2

您考虑过regular expressions吗？

alert('kakkerlak'.match(/k/g).length)

Answer 3

不一定与ES6相关，而是更具功能性的方法，例如：使用filter()似乎很不错：

const countChar = (string, needle) =>
  string.split('')
    .filter(char => char === needle)
    .length;

const countBs = string => countChar(string, 'B');

console.log(countBs('BBC'));
console.log(countChar('kakkerlak', 'k'));

Answer 4

优雅在旁观者的眼中，但通过使用reduce可以进一步减少它：

＆＃13;

＆＃13;

'use strict';

const countChar = (string, ch) => 
  string.split('').reduce((sum, c) => sum + (c === ch), 0);

const countBs = string => countChar(string, 'B');

console.log(countBs('BBC'));
console.log(countChar('kakkerlak', 'k'));

＆＃13;

＆＃13;

＆＃13;

它的工作原理是将字符串转换为字符数组，然后总结该数组中与ch匹配的字符数。我也（ab）使用true转换为1和false转换为0的事实，因此将c === ch添加到运行总和中将添加{{1}如果它匹配，则1如果它不匹配。