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

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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: