JavaScript basic syntax

1. Data type
JavaScript data types
Basic type:
Number: Numeric
String: Strings
Boolean: Boolean type
Special types:
Null: Empty
Undefined: Not defined
Complex Type:
Array: Arrays
Object: Objects

2.String type
Represents text
A sequence of Unicode characters, numbers, punctuation marks
A pair of single or double quotation marks
Special characters need escape characters \, such as: \n,\\,\ ', \ "

3.Number type
No distinction between integral and floating-point values
All numbers are stored in 64-bit floating-point format, similar to double format
Integer:
10 binary integers consist of a sequence of numbers
16 binary data front plus 0x, octal front plus 0
Floating point number:
Use decimal points to record data, such as 3.4,5.6
Record data using an exponent, such as 4.3e23 = 4.3*10^23

3.Boolean type
Only two values: True and False
Also represents 1 and 0
True=1,false=0 in the actual operation
More for structure control statements

4. Implicit conversion of data types
JavaScript is loosely programming language
Variable does not need to specify a data type when declaring
Variable has an assignment operation to determine the data type
Different types of data are automatically converted during the calculation
Number + string: number converted to string
Number + Boolean: True converts to 1,false to 0
String + Boolean value: Boolean converted to string true or False
Boolean + Boolean: Converts a Boolean value to a number 1 or 0

5. Data type Conversion functions
Tostring
Convert to String
All data types can be converted to string types
parseint
Cast to Integer
Returns Nan (not a number) if it cannot be converted
For example parseint ("6.12") returns 6
Parsefloat
Cast to floating point number
If it cannot be converted, it returns Nan
For example parsefloat ("6.12") returns 6.12
typeof
Query value current type, return String/number/boolean/object
For example typeof ("Test" +3) = "string"
IsNaN
Determine if the value is

6. Special data types
Null
Null means "No value" or "no object" in the program
You can clear the contents of a variable by assigning a value of NULL to a variable
Undefined
A variable was declared but never assigned or the object property does not exist

7. Conditional operators
The conditional operator, also known as the "Trinocular"/"ternary" operator, has the following structure:
A Boolean expression? Expression 1: Expression 2
The value of the Boolean expression is evaluated first, and if true, the value of the entire expression is the value of expression 1
If False, the value of the entire expression is the value of expression 2

JavaScript basic syntax