JavaScript Basics (2) variables

JavaScript declares variables with the VAR keyword

var variable name;

Declaration Variable name Considerations:

1. The variable name consists of a letter, a value, a "$" symbol, an underscore
2. Variable names must begin with a letter, a "$" symbol, or an underscore
3. Variable names cannot use JavaScript keywords and reserved words
4. Variable names are case-sensitive

Variables must first be declared and then used

var name = "Tom"; var age;age = 10;

When a variable is not assigned a value, the default is undefined, and the variable can be assigned repeatedly.

Variables can hold any type of value, such as numeric value, String, Boolean, etc.

var a = 5;a = "123"; a = true;

Variables can also be directly assigned using the VAR keyword, such as:

i = 5;

　Note: This creates a variable in a way that does not conform to the specification and creates a global variable.

JavaScript Basics (2) variables