定时器
定时器在javascript中的作用
1、制作动画
2、异步操作
3、函数缓冲与节流
定时器类型及语法
/*
定时器：
setTimeout 只执行一次的定时器
clearTimeout 关闭只执行一次的定时器
setInterval 反复执行的定时器
clearInterval 关闭反复执行的定时器
*/
var time1 = setTimeout(myalert,2000);
var time2 = setInterval(myalert,2000);
/*
clearTimeout(time1);
clearInterval(time2);
*/
function myalert(){
alert('ok!');
}
定时器制作时钟
<script type="text/javascript">
window.onload = function(){
var oDiv = document.getElementById('div1');
function timego(){
var now = new Date();
var year = now.getFullYear();
var month = now.getMonth()+1;
var date = now.getDate();
var week = now.getDay();
var hour = now.getHours();
var minute = now.getMinutes();
var second = now.getSeconds();
var str = '当前时间是：'+ year + '年'+month+'月'+date+'日 '+toweek(week)+' '+todou(hour)+':'+todou(minute)+':'+todou(second);
oDiv.innerHTML = str;
}
timego();
setInterval(timego,1000);
}
function toweek(n){
if(n==0)
{
return '星期日';
}
else if(n==1)
{
return '星期一';
}
else if(n==2)
{
return '星期二';
}
else if(n==3)
{
return '星期三';
}
else if(n==4)
{
return '星期四';
}
else if(n==5)
{
return '星期五';
}
else
{
return '星期六';
}
}
function todou(n){
if(n<10)
{
return '0'+n;
}
else
{
return n;
}
}
</script>
......
<div id="div1"></div>
定时器制作倒计时
<script type="text/javascript">
window.onload = function(){
var oDiv = document.getElementById('div1');
function timeleft(){
var now = new Date();
var future = new Date(2016,8,12,24,0,0);
var lefts = parseInt((future-now)/1000);
var day = parseInt(lefts/86400);
var hour = parseInt(lefts%86400/3600);
var min = parseInt(lefts%86400%3600/60);
var sec = lefts%60;
str = '距离2016年9月12日晚24点还剩下'+day+'天'+hour+'时'+min+'分'+sec+'秒';
oDiv.innerHTML = str;
}
timeleft();
setInterval(timeleft,1000);
}
</script>
......
<div id="div1"></div>
作业计算器
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>计算器</title>
<script type="text/javascript">
window.onload = function(){
var oInput01 = document.getElementById('input01');
var oInput02 = document.getElementById('input02');
var oSelect = document.getElementById('select');
var oBtn = document.getElementById('btn');
oBtn.onclick = function(){
var val01 = oInput01.value;
var val02 = oInput02.value;
//不做此判断会弹出“NaN”
if(val01=="" || val02==""){
alert('输入框不能为空！');
return;
}
if(isNaN(val01) || isNaN(val02)){
alert('请输入数字！');
return;
}
switch(oSelect.value){
case '0':
alert((parseFloat(val01)*100 + parseFloat(val02)*100)/100);
break;
case '1':
alert((parseFloat(val01)*100 - parseFloat(val02)*100)/100);
break;
case '2':
alert((parseFloat(val01)*100) * (parseFloat(val02)*100)/10000);
break;
case '3':
alert((parseFloat(val01)*100) / (parseFloat(val02)*100));
break;
}
}
}
</script>
</head>
<body>
<h1>计算器</h1>
<input type="text" name="" id="input01" />
<select id="select">
<option value="0">+</option>
<option value="1">-</option>
<option value="2">*</option>
<option value="3">/</option>
</select>
<input type="text" name="" id="input02" />
<input type="button" name="" value="计算" id="btn" />
</body>
</html>
作业while
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>投资的年利率</title>
<script type="text/javascript">
var money = 1000;
var count = 0;
while(money < 5000){
money *= 1.05;
count++;
}
console.log("一共需要" + count + "年");
</script>
</head>
<body>
</body>
</html>
作业for
<html lang="en">
<head>
<meta charset="UTF-8">
<title>奇数之和</title>
<script type="text/javascript">
/*打印1-100之间所有奇数之和*/
//保存奇数之和
// var sum = 0;
//打印1-100之间的数
for(var i=1,sum=0; i<=100; i++){
//判断i是否是奇数
//不能被2整除的数是奇数
if(i % 2 != 0){
//如果i除以2有余数则证明i是奇数
// console.log(i);
sum += i;
}
}
console.log("奇数之和为：" + sum);
</script>
</head>
<body>
</body>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>7的倍数</title>
<script type="text/javascript">
/*打印1-100之间所有7的倍数的个数及总和*/
//定义一个变量，来保存总和
var sum = 0;
//定义一个计数器，来记录数量
var count = 0;
//打印1-100之间的数
for(var i=1; i<=100; i++){
//判断i是否是7的倍数
if (i % 7 == 0) {
// console.log(i);
sum += i;
//使计数器自增
count++;
}
}
console.log("总和为：" + sum);
console.log("个数为：" + count);
</script>
</head>
<body>
</body>
