JavaScript的prompt用法

<!DOCTYPE html><html><head><meta charset="utf-8"><title></title></head><body><input type="button" onclick="add()" value="计算累加" /><script type="

苦涩精灵

4644人浏览 · 2020-06-14 07:57:28

苦涩精灵 · 2020-06-14 07:57:28 发布

<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
	</head>
	<body>
			<input type="button" onclick="add()" value="计算累加" />
				
				<script type="text/javascript">
					function add() {
						var pattern = /^\+?[1-9][0-9]*$/;
						var N = prompt("请输入正整数N:", "")
						if (N != null && N != " " && (pattern.test(N) == true)) {
							var sum = 0;
							for (var i = 1; i <= N; i++)
								sum += i;
								document.writeln("<b>计算1+2+3+...+N</b></br>");
							document.write("1+...+" + N + "=" + sum);
						} else
							alert("请重新输入正整数N!");
					}
				</script>
	</body>
</html>

Demo:
在这里插入图片描述