如何使用JavaScript添加、减去或乘两个变量？
如何使用JavaScript添加、减去或乘两个变量？
提问于 2016-05-21 04:58:45
<!DOCTYPE html>
<head><title> test ! </title>
<link rel="stylesheet" type="text/css" href="css/bootstrap.min.css" />
<link rel="stylesheet" type="text/css" href="css/index.css" />
</head>
<html>
<body>
<div class="container">
first number : <input class="form-control" id="num1" />
<br>
second number : <input class="form-control" id="num2" />
<br>
<select id="mathtype">
<option value="add"> addition </option>
<option value="sub"> subtraction </option>
<option value="mul"> multiplication </option>
</select>
<br><br>
<button class="btn btn-primary" onclick="submit()" > submit </button>
<br><br>
<input type="text" id="output" >
</div>
</body>
<script src="js/jquery-1.9.1.js"></script>
<script>
function submit(){
var mathtype = document.getElementById['mathtype'];
if (mathtype == add ) {
return num1 + num2;
} else if (mathtype == sub ) {
return num1 - num2;
} else if (mathtype == mul ) {
return num1 * num2;
}
return true;
}
</script>
</html>我当前的错误：
SyntaxError:函数语句需要一个名称。
我想要制作一个程序，它将根据所选的值(add，sub，mul)执行一个数学操作，在单击submit之后，答案将显示在输入中，其中有一个id "output“。
回答 1
Stack Overflow用户
发布于 2016-05-21 05:02:09
function submit() {
var mathtype = document.getElementById('mathtype').value;
//Get the value of the select element..Correct the typo([])
var num1 = Number(document.getElementById('num1').value);
//Get the value of `num1` input and convert it to type `Number`
var num2 = Number(document.getElementById('num2').value);
//Get the value of `num2` input and convert it to type `Number`
if (mathtype == 'add') {
//Compare with `string` as value of select input will be of type string, you did not have variable `add` to be tested
document.getElementById('output').value = num1 + num2;
} else if (mathtype == 'sub') {
//Compare with `string` as value of select input will be of type string, you did not have variable `sub` to be tested
document.getElementById('output').value = num1 - num2;
} else if (mathtype == 'mul') {
//Compare with `string` as value of select input will be of type string, you did not have variable `mul` to be tested
document.getElementById('output').value = num1 * num2;
}
}<div class="container">
first number :
<input class="form-control" id="num1" />
<br>second number :
<input class="form-control" id="num2" />
<br>
<select id="mathtype">
<option value="add">addition</option>
<option value="sub">subtraction</option>
<option value="mul">multiplication</option>
</select>
<br>
<br>
<button class="btn btn-primary" onclick="submit()">submit</button>
<br>
<br>
<input type="text" id="output">
</div>
注意事项__：详细解释请参阅评论
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/37359066
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