JavaScript split 为空字符串赋予数组大小 1，而不是 0

Question

我想用逗号分割字符串以获取 Node.js 中的数组。

exports.test = function(rq, rs){

   var mailList = "sharan@test.com,pradeep@test.com";
   var arrayList = mailList.split(",");    
   console.log(mailList + " array lenght " + arrayList.length );

   mailList = "";
   arrayList = mailList.split(",");
   console.log(mailList + " array lenght " + arrayList.length );

   mailList = "sharan@test.com,";
   console.log(mailList + " array lenght " + arrayList.length );

   mailList = ",";
   console.log(mailList + " array lenght " + arrayList.length );

   rs.send("test here ");

}

控制台输出为:

sharan@test.com,pradeep@test.com array lenght 2
array lenght 1
sharan@test.com, array lenght 1
, array lenght 1

为什么 JavaScript "".split() 返回一个只有一个元素的数组而不是空数组？

Answer 1

返回的数组包含一个空字符串 ([""])。它以这种方式工作，因为直到第一个匹配项(或字符串末尾)为止的所有内容都作为数组的第一个元素返回。在空字符串的情况下，这是一个空字符串。

如果您考虑一下分割算法的实现可能是什么样子，这是有道理的。可能您从包含当前元素的空字符串开始，然后循环遍历字符串的字母，将它们添加到当前元素，直到到达字符串或分隔符的末尾。然后将当前元素插入结果数组。

如果字符串长度为零，则当前元素将从空字符串开始。您直接到达末尾，因此将空字符串推送到结果数组并返回它。

这也是它应该如何工作的。来自 ECMAScript Language Specification :

If the this object is (or converts to) the empty String, the result depends on whether separator can match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one element, which is the empty String.

来自 Mozilla :

When found, separator is removed from the string and the substrings are returned in an array. If separator is not found or is omitted, the array contains one element consisting of the entire string.

Note: When the string is empty, split() returns an array containing one empty string, rather than an empty array.

如果您不喜欢这种行为，您可以编写自己的版本:

//Return an empty array if string is empty.
//Otherwise return the result of the ordinary split.
split2 = (separator) => this == "" ? [] : this.split(separator);