Overview
Determining the type of a value stored inside a variable is very important in any programming language but in javascript, it is extremely important. This is because a javascript variable can hold values of many types and just by looking at the variable definition, you cannot tell the value which it shall hold. Without knowing the type of value, operations performed on them can lead undesired result. Example, a variable can be written as :
var x = 25;
var x = “codippa”;
Suppose you are adding 5 to the value of v, then it does not make any sense to perform add operation if the value of v is “codippa” and can lead to undesirable results. Thus it is necessary to check the type of value in a variable so that application performs as expected.
How to check type of a value
Javascript has a built-in typeof
operator which returns a string representing the data type of the value being checked. Syntax of typeof
is
typeof operand
where operand is the value or variable whose type is checked by typeof
.
Value Types in javascript
Javascript has a wide range of data types. They are:
- String : Represents string values. Example, ‘codippa’, “java”, “javascript” etc.
- Number : Represents a numeric value. It can be an integer, a decimal or a fraction. Example, 10, 4.5, 5/6 etc.
- Boolean : A true or false value.
- Undefined : When variable has not been assigned a value, it is undefined.
- Null : Represents a
null
value. - Object : There are many types which are objects in javascript. These include Arrays, Functions, Date, Regular Expression etc.
Possible return types of typeof
Following table shows the actual data type of a value(from among those described above) and its corresponding value returned by typeof
operator
Data Type | typeof Return Value |
---|---|
String | “string” |
Number | “number” |
Boolean | “boolean” |
Undefined | “undefined” |
Null | “object” |
Object(Function, Array, Date etc.) | “object” |
typeof Examples
Following is a collection of some examples of typeof
usage on values of different data types and the value returned by typeof
. First column shows the usage of typeof
on values of various data types, Second column represents the actual data type of the value whose type is checked and Third column contains the string returned by typeof
operator on this value.
Expression | Actual Data Type | typeof Return Value |
---|---|---|
typeof ‘codippa’ | String | “string” |
typeof 50 | Number | “number” |
typeof true | Boolean | “boolean” |
typeof undefined | Undefined | “undefined” |
typeof function(){ } | Function | “object” |
typeof (33) | “Number” | “number” |
typeof new Date() | Object | “object” |
typeof null | Object | “object” |
typeof Number(6) | Number | “number” |
Hope this post made you learn something about checking the type of a value in javascript.
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