Note 003: Basic data types, operators, control statements

One, variable

1. Variable name: A combination of letters, numbers, underscores, and dollar signs that cannot begin with a number. is case sensitive.

2, declaring variables: var variable name = variable value;

Second, operator

1, arithmetic operators: +-*/(non-divisible)% (modulo) + +--+ = =

III. Basic data types

1. Basic data type: Number , string , boolean, undefined, null

undefined: non-existent variable

null: No value or null value

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2. typeof returns a string of data type

3, the value of the special values:

• Infinity 1e309
• -infinity 5e-324

typeof Infinity ==> "number"

Infinity-infinity ==>nan: (not digital)

• Infinity The result of arithmetic running with any other operand is also equal to infinity

Infinity+20 ==>infinity

• nan Special number : Nan is contagious, there is a nan in arithmetic operation, the whole result is Nan

typeof NaN ==> "number"

1+2+nan==>nan

Note 003: Basic data types, operators, control statements