JavaScript data types and type conversions

JavaScript data types

Boolean (Boolean), number (numeric), string (String), Undefined (undefined), null (Null object), object (object type), Function

Reference type: object, array, function.

raw Data type: numeric, Boolean, NULL, string

variables of the original type cannot add members dynamically:

<script type= "Text/javascript" >        var n= ' I'm so Handsome ';        N.age=100;        alert (n.age); // The result is undefined    . </script>

objects of reference types can add members dynamically:

<script type= "Text/javascript" >        var n=New String (' Sean ');        N.age=100;        alert (n.age); //Results are  -    </script>

The variable is not the object to see if there is a new (so less rigorous).

A variable declares that there is no initial value so the result is undefined. belongs to an unknown state

A variable is assigned a value of NULL. Represents an object that does not exist.

typeof

typeof used to view the types of variables

<script type= "Text/javascript" >varn1=10; varN2=true; varn3= ' Hello '; varN4; varn5=NULL; varn6=NewObject (); Alert (typeofN1);//This can be done, but it is easy to lose a single space, causing errorsAlerttypeof(n2));//BooleanAlerttypeof(n3));//stringAlerttypeof(N4));//undefinedAlerttypeof(N5));//type is displayed as Object, why, null represents an empty object, object is of typeAlerttypeof(N6));//ObjectAlert (String (N5));//use string to display the N5 in the form of strings. If n5=null, then this object cannot call any method. </script>

instanceof

Instanceof Determines whether an object is a reference type

<script type= "Text/javascript" >        var time=New  Date ();         instanceof Date); // true        instanceof Object); // true,date are object objects    </script>

Small case:

<script type= "Text/javascript" >varS1= ' I'm not handsome '; varS2=NewString (' I'm really not handsome ')); Alert (S1instanceofString);//False,s1 is the original type, and the instanceof front should be a reference type variableAlert (s2instanceofString);//true,new out of a string object that must be trueAlert (S1instanceofObject);//false,instanceof should be a reference-type variable beforeAlert (s2instanceofObject);//true, regardless of the type of object, that belongs to typeAlert (typeofS1);//The string type, why it is a lowercase string, just display in the form of a character. AlerttypeofS2);//object type, one of new objects</script>

Type conversions

parseint (ARG) converts the specified string to an integer
Parsefloat (ARG) converts the specified string into a floating-point number
Number (ARG) converts the given value (any type) to a digit (which can be an integer or a floating point), and the entire value, not the partial value, is converted. If the string cannot be fully converted to an integral type, Nan is returned. (Not a number)
IsNaN (ARG), determines whether ARG is a non-numeric (Nan), and Nan is not equal to Nan.
String (ARG) converts the given value (any type) to a string;
Boolean (ARG) converts the given value (any type) to a Boolean type;

<script type= "Text/javascript" >varN1= ' 10 '; Alert (parseint (N1)+10);// -        varN2= ' 10ASD ';//can be identified as the number tenAlert (parseint (n2) +10);// -        varn3= ' ADSAS10JK ';//not recognizedAlert (parseint (n3) +10);//NaN        varn4= ' 321QQW ';//As above , numbers begin with letters that are recognized as numbers, and numbers are not recognized at the beginning of a letter. Alert (parseint (n4,8));//The binary conversion, converting octal to decimal, converting 8 to 16, which translates from 16 binary to decimal        varx1= ' 3.1415926KKSD ';//As above , numbers begin with letters that are recognized as numbers, and numbers are not recognized at the beginning of a letter. Alert (parsefloat (x1) +1);//4.1415926, convert to floating point        varnum1= ' 99 '; Alert (number (NUM1)+1);// -        varNum2= ' 99a '; Alert (number (NUM2)+2);//NaN        varnum3= ' a99d '; Alert (number (NUM3)+3);//NaNAlert (Number (false));//0Alert (Number (true));//1Alert (number (' 1.2.3 '));//NaNAlert (Number (NewObject ()));//NaNAlert (Number (NewDate ()));//1433944956084Alert (Number (NewDate (). tolocaletimestring ()));//NaN        //the test learned that number () is more rigorous and does not identify         //Nan, because the conversion may occur Nan, make a decision before use is not Nan        varn8= ' 12a '; if(IsNaN (Number (n8))) {//isNaN used to determine not a number .Alert (' Yes, sure is not a number ');//as a result, the alert triggers}Else{alert (' Yes, it's a number '); }        //nan and Nan are not equal        varn9= ' 12a '; varm9= ' Ads2 '; Alert (number (N9)==number (M9));//false                //String (ARG) to convert the given value (any type) to a string        vars1=100; Alert (String (S1));// -        varS2=NULL; Alert (String (S2));//NULL        varS3; Alert (String (S3));//undefined                 //String () is equivalent to the ToString () method of the calling object.         //Special column: When the object is null or undefined, the call to ToString () causes an error, and string () can be converted successfully.         vars4=undefined; Alert (s4.tostring ());//Error        vars5=NULL; Alert (s5.tostring ());//Error         varb= ' ads ';        Alert (Boolean (b)); //Boolean (ARG) converts the given value (any type) to a Boolean type</script>

JavaScript data types and type conversions