JavaScript Basic Learning 20 Q (a)

1.cmd Operation Node
E:node carriage return Console.log ("1");
E:node Haha.js Enter (to CD to the directory where the file is located)
2. Browser Two kinds of tools:
1. Typesetting Engine: Loading HTML/CSS
2. Explanation Engine: Run JS script

3. Events (attributes): Elements can respond to different interactions based on different actions of the mouse or keyboard

The position of the 4.script placement affects the program result placed behind the body
Ensure full page load (within 7s pages must be loaded complete)

5. The use of a single revision everywhere in the definition takes effect
All repeated code blocks are encapsulated into a method
Method: A set of code sequences that perform a specialized function
6. Debugging Debug Bugs? --->f12
The error only affects the current script block after the error location is affected,
7.ECMAScript (core syntax) +dom (Action Web page) +bom (Operation browser window) =javascript
8. Annotations also take account of web traffic production environment
9. The variable program is an IPO that runs in memory (input process output)
Variables are spaces in memory that are specifically for storing data
10.Number rounding error. Fixed ()
11.String charCodeAt () Unicode: Number of characters in all language text because computers only know numbers
12. Escape character: \ t tab. \ nthe line break
13. Data type conversions:
Implicit conversions: Only consider +: as long as there is a string to participate in the result is a string, if there is no string result is the number true turns 1 false to 0
Cast: ToString () Number ()
parseint () reads the integer portion starting from the first character to read from the beginning of a number to a number that is not a digit ending ignoring the first character that is not a number returns Nan
14. Arithmetic operations: Any type of subtraction will be converted to a number if you cannot go back to nan 100-"" =100 ("" false-->0)
15. Division operation divisor is 0 result Infinity (number) 0/0 NaN
16. String size is Unicode encoded with "He (Llo)" < "Hi (69)"
Any type and number comparison are converted into numbers
The 17.undefined type is undefined the null type is Object
18.isNaN () is a number or can be automatically converted to a number of return fasle is not a number to return True IsNaN ("ten")//false
19. Logic Operation Short Circuit operation
20.var isalphabet= (c>= "A" &&c<= "Z") | | (c>= "A" &&c<= "Z")

JavaScript Basic Learning 20 Q (a)