--------------------------------New knowledge today---------------- ---------------------
One: Object Class (category)
Object-oriented: Object-oriented is a programming idea, one is the concept of class, and the other is the concept of object
Class: abstract; object: instantiated, concrete; for example, this computer in the computer class is a concrete instantiation of a certain class
(The first letter of the identifier of the class is generally capitalized) (The built-in class of the system and the custom class are all instantiated as objects)
Review data types: basic data types (number string boolean undefined null)
Reference data type: object function arr
Data classification in js: any data in js can find the corresponding category (the first letter is usually uppercase)
Each class in js corresponds to many objects
classes and objects?
A class refers to a certain class, abstract, and an object is instantiated and concrete (an object is a specific class of a certain class)
Object: It is the specificity of a certain class. An object is also called an instance. An object is an unordered collection of attributes (a collection is a container)
In addition to using built-in objects in js, you can create objects yourself
There are two ways to create objects:
The literal way (that is, the way of key-value pairs):
For example:
was however1={
name: "Hahaha",
age：4，
eat：function（）{
consle.log("I will eat")
}；
console.log（dog1.name）；
console.log（dog1.age）；
console.log(dog1.eat());
}
Create objects through the new class new is an operator.
var a=new Number (1) judge whether a belongs to the object of number
（1）console.log（typeof a）object
（2）console.log(a instanceof number) true
Get the properties in the object, object name. property name
The second way to create an object:
var obj=new Object()
obg.name="XXX"
console.log(obj.name)//xxx
Get the method in the object, object name. method name
obj.eat=function(){
console.log("eat ...")
}
obg.eat();
Second, the commonly used classes in js
Understand the built-in classes of js?
Date class : Provides date-related operations
year getFullYear, month getMonth, day getDate hour getHours, minute getHours, second getSecond
Math class: (no need for new) Provide math-related operations random floor ceil round
three arrays
1) An array is a collection of ordered data, two ways to create an array?
(1) By means of literal quantity
var arr1=[10, 20, 20, 31, "Zhang", "", "zhihuimin"]
(2) Instantiation, that is, a new array
var arr2=new Array（“a”，“b”，“c”）；
2) How to judge whether a data is an array?
console.log（arr instanceof Array）；true
console.log（Array.isArray（arr）；true
console.log(arr typeof Array); object
3) Pay attention to details:
When giving Array a data, if it is a numeric type, it means returning an empty array of the length
The index starts from 0 and increases sequentially, which can be discontinuous
Any type of data can be placed in the array
Arrays are dynamic and can grow or shrink according to the length of the array.
4) Operation array
CRUD:
var arr =new Array(a,b,c,d)
access:
console.log(arr[0])//a
Add to:
arr【4】=e
console.log(arr)//[a,b,c,d,e]
Modify element:
arr【2】=123；
console.log(arr)//[a,123,c,d,e]
The property of the array: length
The length of the array can be obtained by the array name.length
console.log (arr.length) to get the length of the array
four strings
1) Two ways to create a string
by literal means
var s1 = "Hello";
console.log（typeof s1)//string
via new a class
var s2=new String("zhang")
console.log(typeof s2)//object
console.log(s2 instanceof string)//true
Five common methods in arrays and strings
array
通过数组方法操作数组？
push 在末尾追加元素 返回新数组长度 改变原数组
unshift 在开头追加元素 返回新数组长度 改变原数组
pop 删除末尾元素 返回被删除的元素 改变原数组
shift 删除开头元素 返回被删除的元素 改变原数组
reverse 将数组反转 返回反转后的数组 改变原数组
sort 把数组中的元素进行排序 返回排序后的数组 改变了原数组 如果需要对数组中的数字进行排序，需要传递一个比较函数，比较函数有两个参数，如果返回第1个参数-第2个参数，是升序， 如果返回第2个参数-第1个参数，是降序
slice 用来截取数组的 返回一个新数组 不改变原数组
toString 把数组转成字符串 返回一个字符串 不改变原数组
join 把数组转成字符串 返回字符串 不改变原数组
concat 多个数组连接成一个数组 返回连接后的新数组 不改变原数组String method:
concat returns a string starting from the specified position to the specified number of characters (without changing the original string)
Find: (do not change the original string)
charAt : returns the specified character of the value
charcodeAt: returns the ascii code of the character specified by the value
indexof: Returns the index (from left to right) of the first occurrence of the character with its specified value
lastindexof: Returns the index of the last occurrence of the character with its specified value (from right to left)
search: returns the index corresponding to the character, if not found, returns -1
intercept
substr: returns the characters from the specified position to the specified number of characters
substring: returns a subset from the start index to the end index (end is not intercepted) (not possible) (start is negative and turns to zero)
slice: returns a subset from the start index to the end index (end is not intercepted) (can be used in an array) (take negative to length+start, length+end processing)
case conversion
toLowercase converts the string to lowercase and returns
toUppercase converts the string to uppercase and returns
replace
replace returns the new string after replacement
turn array
split: use the specified delimiter to split the string object into a string array (without a delimiter, it will be converted to an element in an array by default)