有人可以解释document.getElementById("demo")下面的例子中的行吗？
我理解getElementById获取了demo的id,但id是在这段代码中<p id="demo"></p>究竟是<p id="demo"></p>做什么的？
document.getElementById("age") 很清楚,因为它获得了年龄的id作为输入.
function myFunction() {
var age,voteable;
age = document.getElementById("age").value;
voteable = (age < 18)? "Too young" : "Old enough";
document.getElementById("demo").innerHTML = voteable;
}<p>Click the button to check the age.</p>
Age:<input id="age" value="18" />
<p>Old enough to vote?</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>