parses the string to create an integer value

Description

parseInt() function examines the string to see if it matches a number pattern.

parseInt() uses the following rules to convert string to an integer.

• The parseInt() function ignores leading white space and it checks the string character by character.
• If this first non-white space character isn't a number, the minus sign, or the plus sign, parseInt() returns NaN.
• The parseInt() function returns NaN for empty string, while Number() function returns 0.
• If the first character is a number, plus, or minus, then the checking continues until the end of the string is reached or a non numeric character is found. For instance, "1234asdf" is converted to 1234 because "asdf" is ignored.
• When the string begins with "0x", it is interpreted as a hexadecimal integer.
• If a string begins with "0" followed by a number, it is interpreted as an octal value.

Example

var num1 = parseInt("1234blue");    //1234
console.log(num1);/*from  w ww. j av  a  2  s .c om*/
var num2 = parseInt("");            //NaN
console.log(num2);
var num3 = parseInt("0xA");         //10 - hexadecimal
console.log(num3);
var num4 = parseInt(22.5);          //22
console.log(num4);
var num5 = parseInt("70");          //70 - decimal
console.log(num5);
var num6 = parseInt("0xf");         //15 - hexadecimal
console.log(num6);
//56 (octal) in ECMAScript 3, 0 (decimal) in ECMAScript 5
var num = parseInt("070");
console.log(num);

The code above generates the following result.

radix

parseInt() provides a second argument: the radix.

For hexadecimal format, the radix is 16.

console.log(parseInt("0xAE", 16));

The code above generates the following result.

The leading "0x" is not necessary by providing the hexadecimal radix:

console.log(parseInt("AE", 16));
var num2 = parseInt("AF");            //NaN
console.log(num2);

The code above generates the following result.

Most of the time you'll be parsing decimal numbers, so it's good to always include 10 as the second argument.

var num1 = parseInt("10", 2);         //2 - parsed as binary
console.log(num1);// w ww.ja v a 2  s.  c om
var num2 = parseInt("10", 8);         //8 - parsed as octal
console.log(num2);
var num3 = parseInt("10", 10);        //10 - parsed as decimal
console.log(num3);
var num4 = parseInt("10", 16);        //16 - parsed as hexadecimal
console.log(num4);