<香港科技大学html+css+js课堂笔记>week2--javaScript第二部分
6.选择语句：
if...else if...else...
switch...case...default...
EG1:
<!doctype html>
<html><head><script>
var user_name;
user_name=prompt("What is your name?");
if (user_name == "dave")
alert("Great name!");
else if (user_name == "jogesh")
alert("Pretty good name!");
else if (user_name == "oz")
alert("Excellent name!");
else
alert("Your name isn't great, never mind...");
</script></head></html>
EG2:
<!doctype html>
<html>
<head>
<script>
var user_name=prompt("What is your name?");
switch(user_name) {
case "dave":
alert("Great name!");
break;
case "jogesh":
alert("Pretty good name!");
break;
default:
alert("Your name isn't great, never mind...");
}
</script>
</head>
</html>
7.循环语句：
while...
do...while(condition);
result = text.indexOf("at");
Eg1:
<!doctype html>
<html><head>
<title>Example of while()</title>
<script>
var response, finished;
finished=false;
alert("Rossiter is a great name.");
while (!finished){
response=prompt("Do you agree?");
if (response.indexOf("y")==0)
finished=true;
}
</script>
</head></html>
Eg2:
<!doctype html>
<html><body>
<script>
function show_money() {
alert("In the function, the value is: "+ money);
}
var money = 99;
alert("In the main part, the value is: "+ money);
show_money();
alert("In the main part, the value is: "+ money);
</script>
</body></html>
8.局部变量和全局变量：
全局变量：未声明自动转为全局变量;
Eg:
<!doctype html>
<html><body>
<script>
function show_money() {
money = 2; //money全局变量
alert("In the function, the value is: "+ money);
}
show_money();
alert("In the main part, the value is: "+ money);
</script>
</body></html>
9.布尔值与逻辑运算符：
True、False ||、 &&、!
Eg:
<html><body><script>
var you_are_rich = false;
var you_have_partner = true;
var you_have_flat = true;
var life_is_fantastic = you_are_rich && you_have_partner && you_have_flat;
alert("life is fantastic is " + life_is_fantastic);
you_are_rich = true;
life_is_fantastic = you_are_rich && you_have_partner && you_have_flat;
alert("life is fantastic is now " + life_is_fantastic);
</script></body></html>
10.数组：
var pets = ["Dog", "Cat", "Rabbit"];
var pets = new Array(10);
数组相关函数：
1》join(separator):Use array.join(separator) to convert array into string.
separator 默认为‘,’
Eg:
var pets = ["Dog", "Cat", "Rabbit"];
alert(pets.join(" and "));
// This shows "Dog and Cat and Rabbit"
2>alert(pets[2]); pets[2]="Pig";
3>pets.length;
4>pets.push("Pig")；添加“pig”到结尾；索引自动更新；
5>pets.unshift("pig");在数组开头添加“pig”;
6>pets.pop(); 从数组中删除结尾元素，返回值为删除元素；
7>pets.shift();从数组开头删除元素，返回值为开头元素。
8>pets.concat(array2);合并两个数组
Eg:
var pets = ["Dog", "Cat", "Rabbit", "Hamster"];
var primes = [2, 3, 5, 7, 11];
var result = pets.concat(primes);
// result is ["Dog", "Cat", "Rabbit", "Hamster",
// 2, 3, 5, 7, 11]
11.
1>随机数的产生：
var random_number = Math.random();
2>得到随机数范围：
random_number = Math.random() * max_value; [0, max_value)
3>截取小数的小数部分(不四舍五入)：
Math.floor(2.154386) = 2;