JS data types -NaN, Boolean, null, undefined,object

NaN

NaN is the number type, it's not equal to itself, isNaN() to determine if the value in parentheses isNaN, if it's NaN, it will return true otherwise it will return false. IsNaN likes NaN, hates numbers NaN must be falseCopy the code

Boolean value

False false false! No, no, or negation can be reversed and converted to a Boolean to quickly know the Boolean value of a data type:!!Copy the code

Null null

1. The element does not exist or cannot fetch an element (script tag does not contain the desired element) 2. Assign an empty address. 3. Null if the re does not match a characterCopy the code

Undefined

Object

Key1 :value1, key2:value Key :0-1-2-3 subscript value: How to obtain the value of each item in the array, using subscripts, counting numbers from 0 and length property can both read and write the regular time... New Object is always available. [] array, subscript, and. Delete properties using delete if there are multiple identical key values, the latter will overwrite the former.Copy the code