<!DOCTYPE html>
<html>
<body>
<p>点击下面的按钮，将代码块循环五次：</p>
<button onclick="myFunction()">点击这里</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x="";
for (var i=0;i<5;i++)
{
x=x + "The number is " + i + "<br>";
document.getElementById("demo").innerHTML=x;
}
}
</script>
</body>
</html>
<!DOCTYPE html>
<html>
<body>
<p>点击下面的按钮，将代码块循环五次：</p>
<button onclick="myFunction()">点击这里</button>
<p id="demo"></p>
<script>
function myFunction()
{
var x="";
for (var i=0;i<5;i++)
{
x=x + "The number is " + i + "<br>";
}
document.getElementById("demo").innerHTML=x;
}
</script>
</body>
</html>
上面两段代码是来自w3school中的一个关于for循环和标签元素赋值的问题的例子，我是之前一直纠结于将document.getElementById("demo").innerHTML=x;放在for循环内外结果为什么一样?
放在外边的情况很好理解，无非是p标签输出了循环到最后的x的结果，即：
The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
而放在里面的情况，我之前一直认为是每循环一次p标签输出一次x的结果，即：
The number is 0
The number is 0
The number is 1
The number is 0
The number is 1
The number is 2
The number is 0
The number is 1
The number is 2
The number is 3
The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
但这样的想法是错误的，因为p标签是闪现了5次输出的结果，最后显示的是最终输出的x结果，而不是把每次的值都显示出来，即：
The number is 0
The number is 1
The number is 2
The number is 3
The number is 4
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原文地址：https://www.cnblogs.com/newcapecjmc/p/11081818.html