执行一个全局替换, 忽略大小写

<p>单击按钮将段落中的“blue”替换成“red”。</p>

<p id="demo">Mr Blue has a blue house and a blue car.</p>

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

<script>

  function myFunction() {

    var str = document.getElementById("demo").innerHTML;

    var n = str.replace(/blue/gi, "red");

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

  }

</script>