JavaScript parseInt Function

In this article, we will dive into JavaScript's parseInt function. As the name suggests, parseInt is a function that is used to parse a string argument and return an integer. This is particularly useful in various situations, such as when converting user inputs into more manageable data types for further processing.

Understanding the Syntax of parseInt

Here's the syntax for the JavaScript parseInt function:

parseInt(string, radix);

The parseInt function takes two arguments: the string to be parsed and an optional radix (or base) for the numeric system you want to use. The radix can be any number between 2 and 36.

Examples of Using JavaScript parseInt

Now, let's dive into some examples of using the parseInt function in JavaScript. The examples below will showcase different ways you can use the function to achieve the desired results.

Example 1: Basic Usage of parseInt
const userAge = '25';
const age = parseInt(userAge);
console.log(age); // Output: 25

In this example, we simply converted a string into an integer using the parseInt function.

Example 2: Using parseInt with a Radix

const hexNumber = 'A3';
const decimalNumber = parseInt(hexNumber, 16);
console.log(decimalNumber); // Output: 163

Here, we've passed the radix (16) as the second argument to parseInt, instructing it to treat the input string as a hex number. The function then returns the decimal representation of the number.

Common Issues with JavaScript parseInt Function

One common issue encountered with JavaScript's parseInt function is incorrect parsing when the radix is not explicitly specified. For example:

const number = '010';
const intNumber = parseInt(number);

console.log(intNumber); // Output: 8

As seen here, omitting the radix caused the string to be treated like an octal number, resulting in an unexpected output. Always remember to specify the radix to avoid such issues.


JavaScript's parseInt function is an essential tool for converting strings into integers, especially when dealing with user inputs or different numeric systems. This comprehensive guide covered the syntax, various usage examples, and potential issues related to parseInt. With this knowledge, you can use the function more effectively in your JavaScript projects.

Recommended Reading