Data types and variables for JavaScript

　JavaScript data types

1. Original Data type:

numeric , such as decimal number, hexadecimal number, octal number, and special value (Infinity, nan), note: NaN cannot compare itself with

String type , such as delimiter, escape character;

the Boolean type .

2. Composite Data type:

Objects (object );

Arrays (array );

function .

3. Special Data Types:

no defined data type undefined;

The null value is Null.

The difference between null and undefined is that undefined means that the variable is not assigned, and null means that the variable is given a null value, and Null is equivalent to a placeholder.

　JavaScript Data type conversions

1. Implicit conversion:

Convert to Boolean type false:

Convert to Numeric Data:

Convert to String Data:

2. Explicit conversion:

Convert to numeric value (by number () to numeric value, converted to integer by parseint (string,radix), parsefloat (tring) to floating-point values):

Convert to a string (converted to a string through a string function):

Convert to Boolean type (cast to Boolean by Boolean function):

　JavaScript variables

1. Declare variables:

Declare variables with the Var keyword;

Variables can be declared at the same time to assign values;

You can declare one variable at a time, or you can declare multiple variables at once;

If only the variable is not assigned a value, the default value is undefined;

If the name of the variable produces an overlay.

Precautions:

Variables are strictly case-sensitive;

Variable names do not contain special characters;

Variable names are best followed by hump marking or underline method;

Variable names are best understood.

2. Storage and release of variables in memory:

Collection method: useless storage unit collection, automatic

Collect content:

Recovery Algorithm.

Data types and variables for JavaScript