why do convert numbers to string in Javascript using tostring method?

Question

I was wondering why do people have to convert numbers to string. What are the practical uses for that kind of conversion? Similarly why do developers use parseInt or parseFloat to convert a string to a number. thanks

Answer 1

Using parseInt and parseFloat is important if you want to do arithmetic operations on a number which is in string form. For example

"42" + 1 === "421"
parseInt("42") + 1 === 43;

The reverse is true when you want to do string operations on values which are currently a number.

42 + 1 === 43
(42 + "") + 1 === 421

Why one would want to do the former or latter though is very scenario specific. I'd wager the case of converting strings to numbers for arithmetic operations is the more prominent case though.

Answer 2

The variable's data type is the JavaScript scripting engine's interpretation of the type of data that variable is currently holding. A string variable holds a string; a number variable holds a number value, and so on. However, unlike many other languages, in JavaScript, the same variable can hold different types of data, all within the same application. This is a concept known by the terms loose typing and dynamic typing, both of which mean that a JavaScript variable can hold different data types at different times depending on context.

With a loosely typed language, you don't have to declare ahead of time that a variable will be a string or a number or a boolean, as the data type is actually determined while the application is being processed. If you start out with a string variable and then want to use it as a number, that's perfectly fine, as long as the string actually contains something that resembles a number and not something such as an email address. If you later want to treat it as a string again, that's fine, too.

The forgiving nature of loose typing can end up generating problems. If you try to add two numbers together, but the JavaScript engine interprets the variable holding one of them as a string data type, you end up with an odd string, rather than the sum you were expecting. Context is everything when it comes to variables and data types with JavaScript.

Answer 3

An example of when converting numbers to strings is useful is when you want to format the number a certain way, perhaps like a currency (1234.56 -> $1,234.56).

The converse is useful when you want to do arithmetic on strings the represent numbers. Say you have a text box were you allow the user to input a number. The value of that text box will be a string, but you need it as a number to do some arithmetic with it, so you would use parseInt and parseFloat .

Answer 4

string -> number :

Think about simple number validation using JS. if you can convert a string into a number, then you can validate that number before posting to a number, or for use in an arithmetic operation.

number -> string :

String concatenation mainly and display purposes. The language will most often use implicit conversion to convert the number into a string anyway, such as:

1 + " new answer has been posted"

Do remember, Javascript is a loosely typed language. This can hide a lot of implicit type-casting that is occurring.