查找字符串 "welcome"

<p id="demo">单击按钮来定位指定文本首次出现的位置。</p>

<button onclick="myFunction()">点我</button>

<script>

  function myFunction() {

    var str = "Hello world, welcome to the universe.";

    var n = str.indexOf("welcome");

    document.getElementById("demo").innerHTML = n;

  }

</script>