The **`parseInt()` function** is a built-in function in JavaScript which allows users to convert a string to an integer value.

# Syntax
The basic syntax of the function is:

## Parameters
The `parseInt()` function takes the following parameters as input:

* **String:** The string to convert to an Integer value
* **Radix:** Specifies the numeral system i.e., the base of the number

Radix is an optional parameter. In case it is not mentioned, the following assumptions are made:
1. If the string begins with **0x**, the base is considered 16 (hexadecimal)
2. If the string begins with **0**, the base is considered to be either 8 (octal) or 10 (decimal), depending on the system implementation
3. For any other starting value of the input string, the base is assumed to be 10 (decimal)

## Return value
If the function parses the string successfully, the integer value is returned. In case the string cannot be converted to an integer value, `NaN` is returned.

> **Note:**
> In case the string starts with a numeric character but is followed by an alpha-numeric character, the string is parsed until the occurrence of the first alphanumeric character
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# Example
Let's look at some examples to understand further how to use the `parseInt()` function:

document.addEventListener("DOMContentLoaded", function () {
 
 // Integer value is returned
 value = parseInt("99"); 
 document.write('parseInt("99") = ' + value + " "); 
 
 // NaN is returned
 value = parseInt("Educative!"); 
 document.write('parseInt("Educative!") = ' + value + " "); 
 
 // Only the number before alphanumeric characters is returned
 value = parseInt("99educative76"); 
 document.write('parseInt("99educative76") = ' + value + " "); 
 
 // First number encountered is returned
 value = parseInt("2019 4 29"); 
 document.write('parseInt("2019 4 29") = ' + value + " "); 

 // Converting number to base 16
 value = parseInt("0x256"); 
 document.write('parseInt("0x256") = ' + value + " "); 

 // Converting number to base 8
 value = parseInt("256", 8); 
 document.write('parseInt("256", 8) = ' + value + " "); 
});

codemirror

How to use the parseInt() function in JavaScript

The parseInt() function in JavaScript converts a string to an integer value, with an optional radix parameter.