JavaScript Judging data Type summary

　Recent projects have encountered some of the JavaScript data types of judgment processing, the Internet to find information, and personally verify the various data types of judgment, here to do a summary!

The data type in JS

1. Numeric (number): Includes integers, floating-point numbers.

2. Boolean Type (Boolean)

3. String type

4. Objects (object)

5. Arrays (Array)

6. Null value (NULL)

7. Undefined (Undefined)

Second, determine the data type of a variable

1, numeric type (number)

The more common methods of judging are:

function Isnumber (val) {     returntypeof'number' ;} var A;isnumber (parseint (a));

But in some cases not, such as the above to judge A, is true, this is obviously wrong:

The variable A is actually Nan, and it cannot be used for numeric operations. So the above function can be modified to:

function Isnumber (val) {    returntypeof'number' & & Isfinite (val);}

This is correct, by the way, by introducing the JavaScript isfinite () function, theisfinite () function is used to check if the parameter is infinite, and if number is a finite digit (or convertible to a finite number), then true is returned. Otherwise, if number is NaN (not a number), or positive, negative infinity, then false is returned.

2. Boolean Type (Boolean)

Boolean type judgment is relatively simple, can be judged by the following methods:

// The judging variable val is not a Boolean type function Isbooleantype (val) {    returntypeof val = = ="boolean" ;}

3. Strings (String)

The judgment of the string type is relatively simple and can be judged by the following methods:

// The judging variable val is not a string type function Isstringtype (val) {    returntypeof val = = = ="string" ;}

4. Undefined (Undefined)

Undefined judgments are relatively simple and can be judged by the following methods:

// Judging the variable val is not undefined function isundefined (val) {    returntypeof val = = ="undefined" ;}

5. Objects (object)

Because when a variable is null, typeof also returns object, so object cannot be judged directly with TypeOf. This should be the case:

// The judging variable is not of type Object function Isobj (str) {    ifnulltypeof'undefined'  ) {        returnfalse;    }         return typeof ' Object ' ;}

6, null value (NULL)

Determine null with val = = = NULL

// determine if the variable is not NULL function IsNull (val) {    return  null;}

7. Arrays (Array)

The array type cannot be judged by typeof. Because when a variable is an array type, typeof returns an object.

Here are two ways to determine the array type:

/*The judgment variable arr is not an array method one*/function IsArray1 (arr) {returnObject.prototype.toString.apply (arr) = = ='[Object Array]';}/*determine if the variable arr is array method two*/function IsArray2 (arr) {if(arr = = =NULL||typeofarr = = ='undefined'){        return false; }    returnArr.constructor = = =Array;}

JavaScript Judging data Type summary