计算Javascript中字符串中出现的字符数 [英] Count the number of occurrences of a character in a string in Javascript
问题描述
我需要计算一个字符串中出现的字符数。
I need to count the number of occurrences of a character in a string.
例如，假设我的字符串包含：
For example, suppose my string contains:
var mainStr = "str1,str2,str3,str4";
我想找到逗号的计数，字符，即3.以逗号分割后的单个字符串的计数，即4。
I want to find the count of comma , character, which is 3. And the count of individual strings after the split along comma, which is 4.
我还需要验证每个字符串即str1或str2或str3或str4不应超过15个字符。
I also need to validate that each of the strings i.e str1 or str2 or str3 or str4 should not exceed, say, 15 characters.
推荐答案
我已更新此答案。我喜欢更好地使用匹配的想法，但速度较慢：
I have updated this answer. I like the idea of using a match better, but it is slower:
console.log(("str1,str2,str3,str4".match(/,/g) || []).length); //logs 3
console.log(("str1,str2,str3,str4".match(new RegExp("str", "g")) || []).length); //logs 4
如果您事先知道要搜索的内容，请使用正则表达式文字，否则可以使用 RegExp 构造函数，并将 g 标记作为参数传递。
Use a regular expression literal if you know what you are searching for beforehand, if not you can use the RegExp constructor, and pass in the g flag as an argument.
匹配返回 null ，没有结果，因此 || []
match returns null with no results thus the || []
我在2009年做出的原始答案如下。它会不必要地创建一个数组，但使用拆分更快（截至2014年9月）。我很矛盾，如果我真的需要速度，毫无疑问我会使用分组，但我更愿意使用匹配。
The original answer I made in 2009 is below. It creates an array unnecessarily, but using a split is faster (as of September 2014). I'm ambivalent, if I really needed the speed there would be no question that I would use a split, but I would prefer to use match.
旧答案（来自2009）：
Old answer (from 2009):
如果您正在寻找逗号：
(mainStr.split(",").length - 1) //3
如果你'重新寻找str
If you're looking for the str
(mainStr.split("str").length - 1) //4
@ Lo的答案和我自己的傻瓜 jsperf test 分裂速度提升，至少在Chrome中，但再次创建额外阵列似乎并不健全。
Both in @Lo's answer and in my own silly jsperf test split comes ahead in speed, at least in Chrome, but again creating the extra array just doesn't seem sane.
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