JavaScript parseInt function example to convert a string to integer

JavaScript parseInt function example to convert a string to integer:

In this post, we will learn how to use the parseInt function in JavaScript. The parseInt() function can be used to parse a string and it converts that string to an integer. This method converts the string to integer and returns that value.

Definition of parseInt:

The parseInt method is defined as like below:

parseInt(str)
parseInt(str, radix)

Here,

str is the first argument, i.e. the string value to parse. If the argument is not a string, it is converted to a string. Internally, ToString method is used to convert that parameter to a string. If there are any leading whitespaces, the argument is ignored.
The second parameter, radix is an optional value. It is the base to do the conversion. We can provide a value between 2 to 36. If the provided value is not a number, it will be converted to a number.

Return value of parseInt:

The parseInt method returns the integer value parsed. If the parse is failed or if any invalid radix is passed, it will return NaN.

Examples of parseInt:

Let’s take a look at the below example:

let arrayOfStrings = [
  "12",
  "13",
  "13.4",
  "   12",
  "   13   ",
  "   13xxy",
  "xxy12",
  "+12",
  "   +13",
  "   -14  ",
  "-16.7",
];

arrayOfStrings.forEach((i) => console.log(`${i} => ${parseInt(i)}`));

It will print:

12 => 12
13 => 13
13.4 => 13
   12 => 12
   13    => 13
   13xxy => 13
xxy12 => NaN
+12 => 12
   +13 => 13
   -14   => -14
-16.7 => -16

As you can see here,

It returns NaN if the string starts with any character.
If there is any blank spaces, or +, -, it ignores.
Since we are not providing the radix value, it takes it as 10.

Examples of parseInt with hexadecimal string:

If we pass any string starts with 0x and if we don’t provide a radix value, it will take it as a hexadecimal value, i.e. radix as 16.

let arrayOfStrings = [
  "0x12",
  "0xAE8"
];

arrayOfStrings.forEach((i) => console.log(`${i} => ${parseInt(i)}`));

It will print:

0x12 => 18
0xAE8 => 2792

If we provide 16 as the radix value, it will print the same output.

let arrayOfStrings = [
  "0x12",
  "0xAE8"
];

arrayOfStrings.forEach((i) => console.log(`${i} => ${parseInt(i, 16)}`));

CodeVsColor

JavaScript parseInt function example to convert a string to integer