1.就近原则
2.具体性原则
3.重要性原则
JavaScript = ECMAScript + BOM + DOM
ES：JavaScript的语法规范
BOM：浏览器对象模型
DOM:文档对象模型
判断是否是闰年
var isOk = true;
window.alert(isOk)
window.alert(!isOk)
var name = window.prompt('请输入用户名:')
if(name != 'null' && name.trim().length > 0){
window.alert('你好,' + name + '!')
}else{
window.alert('大家好!')
}
while不确定循环次数
for 循环的次数不确定
var flag = true;
while(flag){
var yearStr = window.prompt('请输入需要判断的年份：');
var year = parseInt(yearStr);
if(year == yearStr && year > 0){
if(year % 4 == 0 && year % 100 != 0 || year % 400 == 0){
window.alert(year + '是闰年');
}else{
window.alert(year + '不是闰年');
}
flag = window.confirm('是否继续？');
}else{
window.alert('请输入有效年份');
}
}
车牌限号查询
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
*{
margin: 0;
padding: 0;
}
#div1{
margin: 0 auto;
margin-top: 100px;
text-align: center;
}
#carno{
width: 400px;
height: 30px;
font: 30px/36px;
text-align: center;
border: none;
border-bottom: 1px solid pink;
outline: none;
}
#button1{
color: white;
font: 25px/36px;
width: 90px;
height: 36px;
border: none;
background-color: deepskyblue;
outline: none;
}
#button2{
color: white;
font: 25px/36px;
width: 90px;
height: 36px;
border: none;
background-color: deeppink;
outline: none;
}
#result{
width: 640px;
margin: 0 auto;
text-align: center;
font: 25px/36px arial;
}
</style>
</head>
<body>
<div id="div1">
<!--<label>请输入车牌号：</label><br />-->
<input type="text" name="" id="carno" value="" placeholder="输入车牌号"/>
<input type="button" id="button1" value="查 询" onclick="showResult()"/>
<input type="button" id="button2" value="清 除" onclick="clearHistory()"/>
</div>
<br />
<hr />
<p id="result"></p>
<script type="text/javascript">
function showResult(){
var input = document.getElementById('carno');
var p = document.getElementById('result');
var carNo = input.value;
var regex = /^[川渝云贵京津沪][A-Z]\s*[0-9A-Z]{5}$/;
if(regex.test(carNo)){
var digitStr = lastDigit(carNo);
if (digitStr){
var digit = parseInt(digitStr);
var day = new Date().getDay();
if(digit % 5 == day || digit % 5 == day - 5){
newStr = carNo + '今日限行！<br>' + p.innerHTML;
p.innerHTML = newStr;
}else{
newStr = carNo + '今日不限行！<br>' + p.innerHTML;
p.innerHTML = newStr;
}
}else{
newStr = carNo + '不是有效车牌！<br>' + p.innerHTML;
p.innerHTML = newStr;
}
}else{
newStr = carNo + '不是有效车牌！<br>' + p.innerHTML;
p.innerHTML = newStr;
}
input.value = '';
}
function lastDigit(str){
for(var index = str.length - 1; index >= 0; index -= 1){
var digitStr = str[index];
if(digitStr >= '0' && digitStr <= '9'){
return digitStr;
}
}
return null;
}
function clearHistory(){
var c = document.getElementById('result');
c.innerHTML = '';
}
</script>
</body>
</html>
