parseInt function to convert string to integer in JavaScript

parseInt(input_string, radix);

input_string:

Input value as string.
Whitespace before and after are ignored.
If the first character can't be converted to number then NaN is returned.

radix:

The base value of mathematical numeral system. Integer between 2 and 36

<script>
document.write(parseInt(2)); // Output 2
document.write("<br>");
document.write(parseInt(2.4)); // Output 2 
document.write("<br>");
document.write(parseInt(-3.9)); // Output -3 
document.write("<br>");
document.write(parseInt('2.4')); // Output 2
document.write("<br>");
document.write(parseInt('-2.4')); // Output -2
document.write("<br>");
document.write(parseInt('Hello')); //Output  NaN
document.write("<br>");
document.write(parseInt('5ab')) // Output 5
document.write("<br>");
document.write(parseInt('ab5')) // Output NaN 
document.write("<br>");
document.write(parseInt(' 50 ')) // Output 50
document.write("<br>");
document.write(parseInt()); // Output NaN
</script>

What is NaN ?

With radix

With different base numbers.

<script>
document.write(parseInt(15,16)) // Output 21, Hexadecimal Number system
document.write("<br>");
document.write(parseInt(15,8)) // Output 13, Octal Number system
document.write("<br>");
document.write(parseInt(5,2)) // Output NaN, Not a Binary Number system
document.write("<br>");
document.write(parseInt(101,2)) // Output 5, Binary  Number system
document.write("<br>");
</script>

By using parseInt function we can convert strings to integer.

Without Radix and string starting with 0X,0x or 0

Without any value for Radix or if Radix = 0 then if input string starts with 0x or 0X then radix is considered as 16 ( hexadecimal number system )

Similarly if input string starts with 0 then radix is considered as 8 ( Octal number system )

In all other cases ( input string starting with any other value ) Radix is assumed as 10 ( decimal system ).

<script>
document.write(parseInt(0XA)) // Output 10 , Hexadecimal Number system
document.write("<br>");
document.write(parseInt(011)) // Output 9 , Octal Number system
document.write("<br>");
</script>

It is always better to specify Radix ( even for decimal number system )

Example of parseInt function

Here is a demo where inputs are used after passing through parseInt function. The output is then considered for calculation.

Enter some numbers with decimal values here. Here is the code of this demo

<script type="text/javascript"> 
function disp_data(){
document.getElementById("a2").innerHTML=parseInt(document.getElementById('t1').value) + parseInt(document.getElementById('t2').value);
}
</script>

<input type=text name=t1 id='t1' > <input type=text name=t2 id='t2' >
<input type=button value='Display Sum' onClick='disp_data()';> 
<div id='a2'  style=" background-color: #c0f0c0; width:200" > Enter two numbers</div>

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parseInt function for string to integer

With radix

Without Radix and string starting with 0X,0x or 0

Example of parseInt function

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