為什么沒(méi)效果
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>計(jì)時(shí)器</title>
<script type="text/javascript">
? var num=0;
? function startCount() {
? ? document.getElementById('count').value=num;
? ? num=num+1;
? ? setTimeout("startCount()",1000);
? }
? startCount();
</script>
</head>
<body>
<form>
<input type="text" id="count" />
</form>
</body>
</html>
2022-03-25
多了一個(gè)“}”花括號(hào)也可能是瀏覽器問(wèn)題吧，我有時(shí)候也有這種問(wèn)題
2017-03-26
這是由于在你剛開(kāi)始的時(shí)候網(wǎng)頁(yè)還沒(méi)有加載完畢，id為 "count"的控件還沒(méi)有加載好，然后你直接執(zhí)行startCount()方法，該方法里的document.getElementById("count")獲取到的對(duì)象為null；所以要想有效果，應(yīng)該在函數(shù)后面不執(zhí)行startCount()，應(yīng)該執(zhí)行setTimeout("startCount()",1000)設(shè)置一個(gè)延時(shí)等待的網(wǎng)頁(yè)的加載。
2017-03-25
<!DOCTYPE html>
<html>
?<head>
? <title> 事件</title>?
? <script type="text/javascript">
?? function count(){
??? var oTxt1 = document.getElementById("txt1").value;
??? var oTxt2 = document.getElementById("txt2").value;
??? var oSlt = document.getElementById("select").value;
??? var result = "";
??? switch(oSlt) {
??????? case "+":
??????????? result = parseFloat(oTxt1) + parseFloat(oTxt2);
??????????? break;
??????? case "-":
??????????? result = parseFloat(oTxt1) - parseFloat(oTxt2);
??????????? break;
??????? case "*":
??????????? result = parseFloat(oTxt1) * parseFloat(oTxt2);
??????????? break;
??????? default:
??????????? result = parseFloat(oTxt1) / parseFloat(oTxt2);
??? }
??? document.getElementById("fruit").value = result;
???
?? }
? </script>
?</head>
?<body>
?? <input type='text' id='txt1' />
?? <select id='select'>
??? ?<option value='+'>+</option>
??<option value="-">-</option>
??<option value="*">*</option>
??<option value="/">/</option>
?? </select>
?? <input type='text' id='txt2' />
?? <input type='button' value=' = ' onclick=count() /> <!--通過(guò) = 按鈕來(lái)調(diào)用創(chuàng)建的函數(shù)，得到結(jié)果-->
?? <input type='text' id='fruit' />??
?</body>
</html>