JS的数据类型

数据类型

• Undefined

• Null

• Boolean

• String

• Symbol

• Number

• Object

解释

• The Undefined type has exactly one value, called undefined. Any variable that has not been assigned a value
  has the value undefined.

• The Null type has exactly one value, called null

• The Boolean type represents a logical entity having two values, called true and false.

• The Symbol type is the set of all non-String values that may be used as the key of an Object property (6.1.7). Each possible Symbol value is unique and immutable.

  Each Symbol value immutably holds an associated value called [[Description]] that is either undefined or a String value.