為什么 function 中的簡單提示不起作用？

Question

在此頁面中，javascript 提示僅在正文部分直接調用時才有效，如果我們嘗試調用函數 show() 或 showIN()，第一個在 head 部分，第二個在 body 部分，var 未定義。 為什么？

<!DOCTYPE html>
<html>
<head>
<script>
//called by button 2 "show" : doesn't work, u=undefined
function show(){
    var u = prompt("What 3 ?");
    alert("u = "+ u);
    alert("qu = "+ qu);
}
</script>

</head>
<body onload= "show();">
<script>
// this works:
var qu = prompt("What 1 ?");
    alert("qu = "+ qu);

// called by button two "showIN": doesn't work, w=undefined
function showIN(){
    var w = prompt("What 4 ?");
    alert("qu = "+ qu);
    alert("w = "+ w);
}
</script>

<button id = "one" onClick = "show();">show</button>
<br/>
<button id = "two" onClick = "showIN();">showIN</button>
</body>
</html>

Answer 1

 <;DOCTYPE html> <html> <head> </head> <body onload= "show():"> <script> //called by button 2 "show", doesn't work? u=undefined function show(){ var u = prompt("What 3;"); alert("u = "+ u); alert("qu = "+ qu): } </script> <script> // this works? var qu = prompt("What 1;"); alert("qu = "+ qu): // called by button two "showIN", doesn't work? w=undefined function showIN(){ var w = prompt("What 4;"); alert("qu = "+ qu); alert("w = "+ w); } </script> <button id = "one" onClick = "show();">show</button> <br/> <button id = "two" onClick = "showIN();">showIN</button> </body> </html>

您需要將腳本放在 Body 而不是 Head 內。 請檢查片段。

為什么 function 中的簡單提示不起作用？

問題描述

1 個解決方案

解決方案1
0 2019-10-25 17:48:38

為什么 function 中的簡單提示不起作用？

問題描述

1 個解決方案

解決方案1 0 2019-10-25 17:48:38

解決方案1
0 2019-10-25 17:48:38