JavaScript parseInt() Function

Last Updated : 22 Nov, 2021

Below is the example of the parseInt() function.

Example:


<script>
    var v1 = parseInt("3.14");

    document.write('Using parseInt("3.14") = '
    + v1 + "<br>");
</script>
Output:
```
Using parseInt("3.14") = 3
```

The parseInt() function is used to accept the string ,radix parameter and convert it into an integer.The radix parameter is used to specify which numeral system to be used, for example, a radix of 16 (hexadecimal) indicates that the number in the string should be parsed from a hexadecimal number to a decimal number. If the string does not contain a numeric value then it returns NaN i.e, not a number.

Syntax:

parseInt(Value, radix)

Parameters: This function accepts two parameters as mentioned above and described below:

Value: This parameter contains a string which is converted to an integer.

radix: This parameter represents the radix or base to be used and it is optional.

Return value: It returns a number and if the first character can’t be converted to a number then the function returns NaN. It actually returns a number parsed up to that point where it encounters a character that is not a number in the specified radix(base).

Below examples illustrate the parseInt() function in JavaScript:

Example 1: The n contains 2018 as ‘@’ is not a Number and parsing stops at that point,further characters are ignored.
```
Input: var n = parseInt("2018@geeksforgeeks");
Output: n = 2018
```

Example 2:

Input: var a = parseInt("1000");
Output: a = 1000(Number)

More example codes for the above function are as follows:

Program 1:

<!DOCTYPE html>
<html>
<body>
    <script>
      
        a = parseInt("100");
        document.write('parseInt("100") = ' +
        a + "<br>");
          
        // It returns a Integer until
        // it encounters Not a Number character
        b = parseInt("2018@geeksforgeeks");
        document.write('parseInt("2018@geeksforgeeks") = ' + 
        b + "<br>");
          
        // It returns NaN on Non numeral character
        c = parseInt("geeksforgeeks@2018");
        document.write('parseInt("geeksforgeeks@2018") = ' + 
        c + "<br>");
          
        // It returns Integer value of a Floating point Number
        d = parseInt("3.14");
        document.write('parseInt("3.14") = ' + d + "<br>");
          
        // It returns only first Number it encounters
        e = parseInt("21 7 2018");
        document.write('parseInt("21 7 2018") = ' + 
        e + "<br>");
      
    </script>
</body>
</html>                    

Output:

parseInt("100") = 100
parseInt("2018@geeksforgeeks") = 2018
parseInt("geeksforgeeks@2018") = NaN
parseInt("3.14") = 3
parseInt("21 7 2018") = 21

Program 2: If the radix is not mentioned in parseInt() function and starting of string contain “0x” than it treated as hexadecimal value. By default radix is 10 (decimal). Note that in line 11 there is ‘8’ which is a character that is not defined in radix 8 numeral system therefore it returns NaN.

<!DOCTYPE html>
<html>
    <body>
        <script>
          
        // Base 10
        a = parseInt("100",10);
        document.write('parseInt("100",10) = ' + 
        a + "<br>");
          
        // Base 8
        b = parseInt("8",8);
        document.write('parseInt("8",8) = ' + 
        b + "<br>");
          
        // Base 8
        c = parseInt("15",8);
        document.write('parseInt("15",8) = ' + 
        c + "<br>");
          
        // Base 16
        d = parseInt("16",16);
        document.write('parseInt("16",16) = ' + 
        d + "<br>");
          
        // Leading and trailing spaces are ignored 
        // in parseInt() function
        e = parseInt(" 100 ");
        document.write('parseInt(" 100 ") = ' + 
        e + "<br>");
          
        // Base 16(hexadecimal)
        f = parseInt("0x16");
        document.write('parseInt("0x16") = ' + 
        f + "<br>");
          
        </script>
      
    </body>
</html>                                

Output:

parseInt("100",10) = 100
parseInt("8",8) = NaN
parseInt("15",8) = 13
parseInt("16",16) = 22
parseInt(" 100 ") = 100
parseInt("0x16") = 22

Supported Browsers:

Google Chrome 1 and above
Edge 12 and above
Firefox 1 and above
Internet Explorer 3 and above
Safari 1 and above
Opera 3 and above

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