Typecasting in Javascript
By: Emiley J.
It’s also possible to convert values using a process called type casting. Type casting allows you to access a specific value as if it were of a different type. Three type casts are available in JavaScript:
-
Boolean(value) – casts the given value as a Boolean
-
Number(value) – casts the given value as a number (either integer or floating-point)
-
String(value) – casts the given value a string
Casting a value using one of these three functions creates a new value that is a direct conversion of the original. This can lead to some unexpected results. The Boolean() type cast returns true when the value is a string with at least one character, a number other than 0, or an object (discussed in the next section); it returns false when the value is an empty string, the number 0, undefined , or null . The following code snippet can be used to test type casting as a Boolean:
var b1 = Boolean(“”); //false – empty string
var b2 = Boolean(“hi”); //true – non-empty string
var b3 = Boolean(100); //true – non-zero number
var b4 = Boolean(null); //false - null
var b5 = Boolean(0); //false - zero
var b6 = Boolean(new Object()); //true – object
The Number() type cast works in a manner similar to parseInt() and parseFloat() , except that it converts the entire value, not just part of it. Remember that parseInt() and parseFloat() only convert up to the first invalid character (in strings), so “4.5.6” becomes “4.5” . Using the Number() type cast, 4.5.6” becomes NaN because the entire string value cannot be converted into a number. If a string value can be converted entirely, Number() decides whether to use parseInt() or parseFloat() . The following table illustrates what happens when Number() is used on various values:
Usage Result
Number(false) 0
Number(true) 1
Number(undefined) NaN
Number(null) 0
Number(“5.5”) 5.5
Number(“56”) 56
Number(“5.6.7”) NaN
Number(new Object()) NaN
Number(100) 100
The last type cast, String() , is the simplest because it can accurately convert any value to a string value. To execute the type cast, it simply calls the toString() method of the value that was passed in, which converts 1 to “1”, true to “true”, false to “false”, and so on. The only difference between type casting as a string and using toString() is that the type cast can produce a string for a null or undefined value without error:
var s1 = String(null); //”null”
var oNull = null;
var s2 = oNull.toString(); //won’t work, causes an error
Type casting is very helpful when dealing with the loosely typed nature of JavaScript, although you should ensure that only proper values are used.
Archived Comments
1. eqienaeto
View Tutorial By: eqienaeto at 2017-01-15 04:11:30
2. Thank you very much for Number() and String(),
I was using it with double not ( !! )
View Tutorial By: Shyam Makwana at 2016-05-09 09:25:28
3. Thank you very much.
View Tutorial By: allcracked at 2013-09-11 19:10:20
4. There is a new library, Typecast.js, to help navigate the typing weirdness in Javascript.
View Tutorial By: Bishop Z at 2013-01-23 19:47:40
5. really good article for type casting for javascript
View Tutorial By: jignesh at 2012-10-31 01:08:38
6. thanks ..it was really helpful.
View Tutorial By: jay at 2012-03-19 04:17:14
7. Typecasting concept helped me alot in solving my prblem. My problem is when I was trying add two num
View Tutorial By: Arun at 2010-09-02 00:23:38
8. Typecasting proved very much helpful to me...esp. when I was adding two variables passed as argument
View Tutorial By: itan at 2010-05-04 01:30:24
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