JS 子字符串频次
请补全JavaScript代码，该函数接受两个参数分别为字符串、子字符串，要求返回子字符串在字符串中出现的频次。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
</head>
<body>
<script>
const _searchStrIndexOf = (str, target) => {
// 补全代码
return str.split(target).length-1
}
</script>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
</head>
<body>
<script>
const _searchStrIndexOf = (str, target) => {
// 补全代码
let index = str.indexOf(target);
let num = 0;
while(index > -1) {
index = str.indexOf(target, index+1);
num++;
}
return num;
}
</script>
</body>
</html>
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