5+5=? Converting values to a string or number in JavaScript

In JavaScript, data can be converted automatically or using functions. In this article, we will learn how data conversion methods work in JS and why adding 5 and 5 together can get 55 instead of 10.

Let's analyze the example:

var a = 5; // number
var b = "5"; // string
var c = a + b; 
alert(c); // 55
alert(typeof(c)) // string

When we add 5 and 5, we expect to see the output — 10. However, we get 55 and see that the data type is not a number, but a string.

JavaScript automatically converted the variable a to a string and concatenated it with the variable b into a single string.

To make the data type expected by the developer, use conversion functions. Let's look at them in detail.

Converting to a string in JavaScript

To convert a number to a string, use the function String().

For example:

var a = 5; // number
a = String(a); // convert the variable а to string
alert(typeof(a)); //string

Converting to a number in JavaScript

To convert data to a number, use the function Number(). Let's try converting a string value 5 to a number.

var a = "5"; // string
a = Number(a); // convert the variable а to number
alert(typeof(a)); //number

If you use strings in mathematical expressions, JavaScript automatically converts variables to numbers.

For example:

var a = "5"; // string
var b = "5"; // string
var c = a / b; 
alert(c);// print 1, that is expected by dividing 5 on 5
alert(typeof(c)); // number

Logical conversion to JavaScript

For logical conversion, use the function Boolean().

Types empty string,NaN, undefined, null — is converted to false.

All other data, such as numbers and strings, is converted to true.

For example:

var a = "null";
alert(Boolean(a)); // false

var a = "0";
alert(Boolean(a)); //true

var a = " "; // space
alert(Boolean(a)); // true

var a = ""; // empty, without spaces and other characters
alert(Boolean(a)); // false

Let's sum up the results

JavaScript can transform data automatically:

• numbers are converted to strings if they are used in expressions with a string;
• if the strings contain numbers and mathematical operations are performed with them, they are converted to numbers.

For conversion, use the functions:

1. String() - converts data to numbers.
2. Number() - converts data to strings.
3. Boolean() - converts data to boolean values true or false.