<香港科技大学html+css+js课堂笔记>week3--JavaScript高级部分

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1.循环语句：

for():

Eg:

for (var index=0; index < continents.length; index++)

for...in... :

Eg:

for (var index in continents)

for...of... :

Eg:

for (var continent of continents)

无限循环：

for ( ; ; ) {
alert("Welcome!");
}

2.控制循环：break 、continue：

break:完全停止循环。

continue：停止本次循环，继续下一次循环。

3.more on arrays:(函数)

1>array.sort() sorts the elements in array:
var pets = ["Dog", "Cat", "Rabbit", "Hamster"];
pets.sort();
// Now pets is ["Cat", "Dog", "Hamster", "Rabbit"]

2>array.reverse() reverses array
The first element becomes the last;
The last element becomes the first
var pets = ["Dog", "Cat", "Rabbit", "Hamster"];
pets.reverse();
// pets is ["Hamster", "Rabbit", "Cat", "Dog"]

3>Use array.indexOf(target) to find the index of
the first occurence of target in array:
If target is not in array, indexOf() will return -1
var pets = ["Dog", "Cat", "Rabbit", "Hamster"];
alert(pets.indexOf("Rabbit")); // This shows 2

If target is not in array, indexOf() will return -1

4>Pass a second value to indexOf()
to control where to start the search
array.indexOf(target, startPosition)

5>Use array.lastIndexOf(target) to find target in array,
starting from the last element in array:
var pets = ["Rabbit", "Dog", "Cat",
"Rabbit", "Hamster"];
alert(pets.lastIndexOf("Rabbit")); // This shows 3

6>Extract part of an array by array.slice(startPosition):

var pets = ["Dog", "Cat", "Rabbit", "Hamster"];
var result = pets.slice(1);
// result is ["Cat", "Rabbit", "Hamster"]

7>You can also set where to stop, by
array.slice(startPosition, endPosition):
var pets = ["Dog", "Cat", "Rabbit", "Hamster"];
var result = pets.slice(1, 3);
// result is ["Cat", "Rabbit"]

8>remove elements from arrays:

array.splice(position, quantity);

var pets = ["Dog", "Cat", "Rabbit", "Hamster"];
var result = pets.splice(1, 1);
// Now pets is ["Dog", "Rabbit", "Hamster"]
// and result is ["Cat"]

**splice() returns the removed element(s)

9>add element(s):

array.splice(position, 0, element):

var pets = ["Dog", "Cat", "Hamster"];
var result = pets.splice(2, 0, "Rabbit");
// Now pets is ["Dog", "Cat", "Rabbit", "Hamster"]
// and result is []

10>replace element(s) :

array.splice(position, quantity, element(s)):

var pets = ["Dog", "Cat", "Hamster"];
var result = pets.splice(1, 1, "Rabbit", "Fish");
// Now pets is ["Dog", "Rabbit", "Fish", "Hamster"]
// and result is ["Cat"].

4.高级的数组操作函数：

1>遍历数组：

可以用循环for,while;

也可用内置函数foreach(function).

Eg:

var pets = ["Dog", "Cat", "Rabbit"];
pets.forEach(alert);
// This shows 3 separate alerts

2>map(function):

<!doctype html>
<html>
<body>
<script>
var square = function(el) { return el * el; }
var numbers = [1, 2, 3, 4, 5];
var results = numbers.map(square);
alert(results); // This shows [1,4,9,16,25];
</script>
</body>
</html>

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