Javascript development technology-Chapter 1 js Data Types

3.1 Basic Data Types
1. string type (string): it consists of unicode characters, numbers, and punctuation marks. In javascript, there is no char character type. A string must be used even if it only represents one character.
2. number: the integer and floating point types are not differentiated.
3. boolean)
3.2 Composite data types
1. array: array element: the data in the array is called an array element.
Array Subscript: numbers starting from 0
Read: arr [0];
Value assignment: arr [1] = 120;
2. Object:
Object Name. attribute name
Object Name. Method Name ()
3.3 Other data types
Function:
1. Functions in javascript are a data type, so they can be stored in variables, arrays, or objects.
2 null: In javascript, null is an independent data type, which indicates no value.
3. undefined indicates undefined. In four cases, undefined is returned.
A. defines a variable but has not been assigned a value.
B. An undefined variable is used.
C. defines an object attribute that does not exist.
D. referenced an array element that does not exist.
3.4 Data Type Conversion
Principle: Convert the data type to the data type required in the current environment.
Implicit conversion rules for javascript Data Types
1. implicit conversion of data types:

Original data type		Number of votes Data Type	Description
String	Non-Null String	Digit acquisition	If the character in a string is a number, it is converted to a string number, for example, "123" is converted to a number of 123, If the character in the string is not a pure number, it is converted to naa
		Boolean	True
	NULL characters	Number Type	0
		Boolean	Flase
	String "true"	Number Type	Nan
		Boolean	True
	Field string "flase"	Number Type	Nan
		Boolean	True
Number Type	Common number	String	Converts a number to a string "number"
		Boolean	Convert the number 0 to false, and convert other numbers to true.
	Nan	String type	Convert to string "Nan"
		Boolean	Convert to false
Boolean	True	String type	Convert to string "true"
		Number Type	Convert to 1
	False	String type	Convert to string "false"
		Numerics	Convert to 0
Null		String type	Convert to string "null"
		Number Type	Convert to 0
		Boolean	Convert to false
Undefined		String type	Convert to string "undefined"
		Number Type	Convert to Nan
		Boolean	Convert to false

2. implicit conversion of alternative data

3. Display and conversion of data types

1. Convert to numeric type

. Nubmer (value) converts value to an integer or floating point number

. ParseInt (value) converts a value to an integer.

. ParseFlaot (value) to floating point

Cannot be converted to numeric type. Nan is returned.

Conversion rules for converting other types to numeric types

Data Type		Description
String	Null String	Use Number () to convert to 0, use parseInt () and parseFloat () to convert to Nan
	String "ture"	Convert to Nan
	String "false	Convert to Nan
	Other strings	If the character in the string is a number, convert it to a number in the character, such as the string "123" It can be converted to 123. If the string is not a pure number, it is converted to Nan
Boolean	True	Use Number () to convert to 0, use parseInt () and parseFloat () to convert to Nan
	False	Use Number () to convert to 0, use parseInt () and parseFloat () to convert to Nan
Null		Use Number () to convert to 0, use parseInt () and parseFloat () to convert to Nan
Undefined		Convert to Nan

2. Convert to boolean

Convert other data types to boolean

Data Type		Yuming
String	Null String	Convert to false
	String "true"	Convert to true
	String "flase"	Convert to true
	Other strings	Convert to true
Number Type	0	Convert to false
	Nan	Convert to false
	Other numbers	Convert to true
Null		Convert to false
Undefined		Convert to false

3. Convert to string type

Convert other data types to string type

Data Type		Description
Number Type	Common number	Converts a number to a string "Number", for example, a Number 1 to a string "1"
	Nan	Convert to string "Nan"
Boolean	True	Convert to string "true"
	Flase	Convert to string "false"
Null		Convert to string "null"
Undefined		Convert to "undefined"