JavaScript Series notes (i) Data types

About JS data types

There are five kinds of simple types: undifined, Null, Boolean, number, String

Complex types have one: Object

Using the typeof operator to get the data type, this operator returns a string

undifined

Boolean

String

Number

Object

function

Type undifined

There is only one value, which is undifined

typeof uninitialized variable, returns undifined

typeof a variable that is not declared, returns undifined

Null type

There is only one value, which is null

typeof Null returns an object

Boolean type

Only two literals: true, False

All types of values have values that are equivalent to these two values

　　

Number Type

Represents a floating-point number with a maximum precision of 17 decimal places, but less precision than an integer

var a = 0.1;

var B = 0.2;

Then: A + b = 0.30000000000000004

Therefore, the use of floating-point numbers need to pay attention to accuracy. You can do this using the following methods:

　　

        functionAccadd (arg1, arg2) {varR1, R2, M, C; Try{r1 = arg1.tostring (). Split (".") [1].length}Catch(e) {r1 = 0 }        Try{r2 = arg2.tostring (). Split (".") [1].length}Catch(e) {r2 = 0} C= Math.Abs (R1-R2); M= Math.pow (10, Math.max (R1, r2))if(C > 0) {            varCM = Math.pow (10, c); if(R1 >R2) {Arg1= Number (arg1.tostring (). Replace (".", "")); Arg2= Number (arg2.tostring (). Replace (".", "")) *cm; }            Else{arg1= Number (arg1.tostring (). Replace (".", "")) *cm; Arg2= Number (arg2.tostring (). Replace (".", "")); }        }        Else{arg1= Number (arg1.tostring (). Replace (".", "")); Arg2= Number (arg2.tostring (). Replace (".", "")); }        return(Arg1 + arg2)/m}

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Range of values:

Number.min_value

Number.MAX_VALUE

Values beyond the range are: Infinity, which can be judged by the isfinite () function.

NaN represents a non-numeric value, which is itself a numeric object

The biggest feature is not equal to any value, even if the Nan,isnan () function can determine whether it is Nan

numeric conversions

Conversion rules for number () functions

　　　　　　　　

parseint ()

Determines whether a numeric pattern is met, ignores the opening space until the first non-null character is encountered, and resolves to the first non-numeric value

parseint (parameter 1,16) means using a 16-binary conversion with the meaning of the parameter as a binary

Parsefloat ()

Use the same method as above

String type

Object type

objects can be created by using new. The object type in JS is the basis for all of its instances. Methods and properties in object are present in more specific objects

Constructor constructor to save the function that creates the current object

hasOwnProperty (PropertyName) checks whether a given property exists in the current object

isPrototypeOf (object) checks whether an incoming object is a prototype of the current object

propertyIsEnumerable (PropertyName) checks whether a given property can use the For-in statement to enumerate

toLocaleString () returns the string representation of an object

ToString () returns the string representation of an object

ValueOf () returns the string, numeric, or Boolean representation of the object. Usually the same as the return value of the ToString () method

　

JavaScript Series notes (i) Data types