<!DOCTYPE html>
<html>
<head>
<script>
function myFunction(a, b) {
return a * b;
document.getElementById("demo").innerHTML = myFunction(4, 3);
}
</script>
</head>
<body>
<p>This example calls a function which performs a calculation, and returns the result:</p>
<p id="demo"></p>
</body>
</html>
[JavaScript] Why? This simple function doesn't work?
2016-05-02 12:22 am
回答 (3)
2016-05-02 12:43 am
Remove document.getElementById( "demo").innerHTML = myFunction(4, 3)
After <p id="demo"></p>, insert
<script>
document.getElementById( "demo").innerHTML = myFunction(4, 3)
</script>
Or use this method —
<head>
<script defer>
function calcDemo() {
document.getElementById( "demo").innerHTML = myFunction(4, 3)
}
function myFunction(a, b) {
return a * b
}
</script>
</head>
<body onload="calcDemo()">
<p>This example calls a function that performs a calculation, and returns the result:</p>
<p id="demo"></p>
After <p id="demo"></p>, insert
<script>
document.getElementById( "demo").innerHTML = myFunction(4, 3)
</script>
Or use this method —
<head>
<script defer>
function calcDemo() {
document.getElementById( "demo").innerHTML = myFunction(4, 3)
}
function myFunction(a, b) {
return a * b
}
</script>
</head>
<body onload="calcDemo()">
<p>This example calls a function that performs a calculation, and returns the result:</p>
<p id="demo"></p>
2016-05-02 1:06 am
JavaScript code is run as it's encountered and while it's running it blocks the web page from loading. The paragraph tag hasn't loaded when you call `document.getElementById()` so your code fails. Move your script tag to just before the closing body tag. That way all the HTML elements will have loaded and be available.
2016-05-02 12:37 am
You have to call the function
myFunction(1,2); for example
myFunction(1,2); for example
收錄日期: 2021-04-18 14:47:41
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20160501162218AAxpijO