1. To achieve such an effect
1.1 There is a mobile phone registration verification function here, I can set the registration page in advance, it is safe,
2 In actual work, if you find that there is no background data, you can only wait (the process is to have an interface, and then use the interface to transfer the data), (1. The core of realizing data interaction is to think about how to define Excuse. 2. What kind of data is the excuse to return, and what is the data format?
2.1
3. For JavaScript, MDN is more authoritative
Link address of MDN: https://developer.mozilla.org/zh-CN/docs/Web/JavaScript 
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript
3.1
4 Click this button to enter and switch to Chinese
4.1
5. Experience Java Script to achieve interactive effects
5.1 Make this effect
5.1 Operation case code
5.2 Get the click button and bind the event
5.3 The meaning of the following function is to take the class, so that it does not change color
5.4 document means to cancel the previous binding, and the next sentence is currently clicked, to be replaced
6. js location, inline, internal and external
7. The inside must be written on the body
7.1
8 internal code
8.1
9 External import through script src file
9.1
10 Inline Java Script Links
10.1
11. Notes on JavaScript
11.1
12 The terminator is;
12.1
13 Input and output syntax
13.1
14. The meaning of this code is to let the page output the content through the js method
14.1
15 write will be written in the body, and the page elements are also inside
15.1
16 The console is used for debugging, and the other is the bullet box
16.1
17console console, the meaning of log log
17.1
18 Use the prompt to get the information entered by the user in the pop-up box
18.1
19 Use of Variables
What is the meaning of the birth of variables? The most valuable thing on a website is user information. How do I store your mobile phone number? I use variables. I know your mobile phone number. Variables are storage data box
Variables store data
19.1
20 let can declare variables
20.1
##
21. Declare a variable
21.1
22 use one = give 18 to age
22.1
23 18 is called a numeric literal
The console successfully outputs 18
Other variable declaration cases
23.1
24 Note that the sub-file format can be used. If you want to change the variable value, you can pass =, but you cannot add let
24.1
25 Declare multiple variables at one time and divide them
25.1
26 Use variables to store data stored by prompt users
26.1
27 How to swap the values of variables
27.1 Procedure for interacting variables
27.2 The first step is to declare three variables
28 JavaScript is to give the right to the left
28.1
29 First give the value of num1 to temp, then give the value of num2 to num1, and then give the value of temp to num2
29.1
30 There will be several G memory sticks in the computer, there are 4G, there are 8G
30.1
31. The hard disk is external memory, 500T, or other. If you want to save a lot of cost, energy is also a cost. The essence of the variable is to apply for the space for storing data from the memory stick.
31.1
32 Variable naming rules, there are only two kinds of symbols_underscore and knife which symbol
32.1
33 The name must be meaningful
33.1
34 Variable name specification, pay attention, numbers cannot start with
34.1
35 1. The difference between let and var, let can be pre-declared, var is an old version, javascript you can use var to declare variables
35.1
36 The meaning of the birth of the array, I want to save the names of 50 classmates at a time, how to save, the array is born
36.1
37 Each array is separated by
37.1
38 Array storage case
38.1 Our array numbers start from zero
39 Using array methods
39.1 Elements, subscripts, numbers
40 mind map is very good
40.1
41. JavaScript can be used to write constants, constant use cases
41.1
42 Java Script data type, numeric number, including decimals
42.1
43 The data type of Java script has priority, () can increase the priority,
43.1
44 How to write the mathematical formula πr square of the area, the original r square is twice multiplied by r
44.1
45 string type, backtick
45.1
46 bug, if you really want to add double quotes inside, use outer single inner double, or outer double inner single
46.1
47 \ Escape character, when you see this symbol, it will print normally for you, use + to splice the string
47.1
48 Use + to concatenate strings
48.1
49 Template strings, when you use strings for splicing, you will find that the bugs in it look too messy, use a knife {} to define variables
49.1
50 Examples of Using Template Strings
50.1
51. Enter your age, and the page will display the entered data
51.1
52. Boolean data
52.1
53 Print undefind in case of no assignment
53.1
54 Use typeof to check the data type
54.1
55 In our form, the default is to take the string
55.1
56 There is a risk here. The data fed back in the form is string type data. If you want to add it, it will be game over. If these two are wages, it will be even more game over.
56.1
57 + As long as there is a string next to it, it can be converted to a string
57.1
58 + positive characters, numbers blue, characters black
58.1
59 + also has a function, which can be converted into a digital type
59.1
60 operation rules
60.1
61. As long as there is a string with a + sign, there will be no problem
61.1
62 display conversion, you tell what type the string is converted to
62.1
63 Examples of converting to data types
