一种简单的方法是将字符串拆分为所需单词，即我们要计算出现次数的单词，然后从部分数中减去1：

function checkOccurences(string, word) {
      return string.split(word).length - 1;
}
const text="Let us see. see above, see below, see forward, see backward, see left, see right until we will be right"; 
const count=countOccurences(text,"see "); // 2

太老了，但我今天需要做这样的事情，只想事后检查一下。对我来说工作很快。

String.prototype.count = function(substr,start,overlap) {
    overlap = overlap || false;
    start = start || 0;

    var count = 0, 
        offset = overlap ? 1 : substr.length;

    while((start = this.indexOf(substr, start) + offset) !== (offset - 1))
        ++count;
    return count;
};

正则表达式（global的缩写）中的g表示搜索整个字符串，而不仅仅是查找第一个出现的字符串。此匹配是两次：

var temp=“这是一个字符串。”；var count=（temp.match（/is/g）| |[]）.length；console.log（计数）；

如果没有匹配项，则返回0：

var temp=“Hello World！”；var count=（temp.match（/is/g）| |[]）.length；console.log（计数）；

看到这篇帖子。

let str = 'As sly as a fox, as strong as an ox';

let target = 'as'; // let's look for it

let pos = 0;
while (true) {
  let foundPos = str.indexOf(target, pos);
  if (foundPos == -1) break;

  alert( `Found at ${foundPos}` );
  pos = foundPos + 1; // continue the search from the next position
}

相同的算法可以被布置得更短：

let str = "As sly as a fox, as strong as an ox";
let target = "as";

let pos = -1;
while ((pos = str.indexOf(target, pos + 1)) != -1) {
  alert( pos );
}

试试看

<?php 
$str = "33,33,56,89,56,56";
echo substr_count($str, '56');
?>

<script type="text/javascript">
var temp = "33,33,56,89,56,56";
var count = temp.match(/56/g);  
alert(count.length);
</script>

我认为regex的目的与indexOf有很大不同。indexOf只需查找某个字符串的出现，而在正则表达式中，您可以使用[a-Z]之类的通配符，这意味着它将查找单词中的任何大写字符，而无需说明实际字符。

例子：

var index=“This is a string”.indexOf（“is”）；console.log（索引）；var length=“This is a string”.match（/[a-z]/g）.length；//其中[a-z]是正则表达式通配符，这就是为什么其速度较慢的原因console.log（长度）；