​x
 
<!DOCTYPE html>
<html>
<body>
​
<h2>JavaScript String 方法</h2>
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<p>如果未找到文本，indexOf() 和 lastIndexOf() 都返回 -1：</p>
​
<p id="demo"></p>
​
<script>
let str = "Please locate where 'locate' occurs!";
document.getElementById("demo").innerHTML = str.indexOf("John");
</script>
​
</body>
</html>
​