javascript - 为什么我的输入框显示未定义？

Question

当我单击调用 showDetails() 函数的提交按钮时，name 和 email 输入框显示未定义。当输入框中有值时也会发生这种情况:

<script type="text/javascript">
function showDetails(){

    var e = document.getElementById("email");
    //var t = document.getElementById("t");
    var n = document.getElementById("name");
    var m = document.getElementById("m");

    var c;
    var r;
    document.getElementById("email").value = c;
    document.getElementById("name").value = r;
    document.getElementById("t").value = "Your name is: "+r+" and your email is: "+c;
}
</script>  

为什么会发生这种情况？

Answer 1

我相信这是因为您将值分配给了未定义。

<script type="text/javascript">
  function showDetails() {

    var e = document.getElementById("email");
    //var t = document.getElementById("t");
    var n = document.getElementById("name");
    var m = document.getElementById("m");

    var c = document.getElementById("email").value; // Here you set it the value = undefined variable
    var r = document.getElementById("name").value;

    document.getElementById("t").value = "Your name is: " + r + " and your email is: " + c;
  }
</script>