parseInt()

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since 20157.

parseInt()

console.log(parseInt("123"));
// 123 (default base-10)
console.log(parseInt("123", 10));
// 123 (explicitly specify base-10)
console.log(parseInt("   123 "));
// 123 (whitespace is ignored)
console.log(parseInt("077"));
// 77 (leading zeros are ignored)
console.log(parseInt("1.9"));
// 1 (decimal part is truncated)
console.log(parseInt("ff", 16));
// 255 (lower-case hexadecimal)
console.log(parseInt("0xFF", 16));
// 255 (upper-case hexadecimal with "0x" prefix)
console.log(parseInt("xyz"));
// NaN (input can't be converted to an integer)

parseInt(string, radix);

string: string ToString parseInt
radix: 2 36 10 radix 10

NaN

parseInt NaN NaN radix radix 10 8 16 For radices above 10, the letters of the alphabet indicate numerals greater than 9. For example, for hexadecimal numbers (base 16), A through F are used.

parseInt radix parseInt

Because some numbers include the e character in their string representation (e.g. 6.022e23), using parseInt to truncate numeric values will produce unexpected results when used on very large or very small numbers. parseInt should not be used as a substitute for Math.floor().

radix undefined 0JavaScript

string "0x" "0X" radix 16
string 0 radix 8 10 8 10 ECMAScript 10 parseInt radix
string radix 10

parseInt NaN

For arithmetic purposes, the NaN value is not a number in any radix. You can call the isNaN function to determine if the result of parseInt is NaN. If NaN is passed on to arithmetic operations, the operation results will also be NaN.

intValue.toString(radix)

`parseInt`

15

parseInt(" 0xF", 16);
parseInt(" F", 16);
parseInt("17", 8);
parseInt(021, 8);
parseInt("015", 10); // parseInt(015, 10); will return 15
parseInt(15.99, 10);
parseInt("15,123", 10);
parseInt("FXX123", 16);
parseInt("1111", 2);
parseInt("15*3", 10);
parseInt("15e2", 10);
parseInt("15px", 10);
parseInt("12", 13);

NaN

parseInt("Hello", 8); // 
parseInt("546", 2); //

-15

parseInt("-F", 16);
parseInt("-0F", 16);
parseInt("-0XF", 16);
parseInt(-15.1, 10);
parseInt(" -17", 8);
parseInt(" -15", 10);
parseInt("-1111", 2);
parseInt("-15e1", 10);
parseInt("-12", 13);

4

parseInt(4.7, 10);
parseInt(4.7 * 1e22, 10); // Very large number becomes 4
parseInt(0.00000000000434, 10); // Very small number becomes 4

224:

parseInt("0e0", 16);

radix

ECMAScript 3 ECMAScript 5 javascript str 0 radix

parseInt("0e0"); // 0
parseInt("08"); // 0, '8' is not an octal digit.

ECMAScript 5 octal interpretation

The ECMAScript 5 specification of the function parseInt no longer allows implementations to treat Strings beginning with a 0 character as octal values. ECMAScript 5 states:

The parseInt function produces an integer value dictated by interpretation of the contents of the string argument according to the specified radix. Leading white space in string is ignored. If radix is undefined or 0, it is assumed to be 10 except when the number begins with the character pairs 0x or 0X, in which case a radix of 16 is assumed.

This differs from ECMAScript 3, which discouraged but allowed octal interpretation.

Many implementations have not adopted this behavior as of 2013, and because older browsers must be supported, always specify a radix.

function

code Regular expression

filterInt = function (value) {
  if (/^(\-|\+)?([0-9]+|Infinity)$/.test(value)) return Number(value);
  return NaN;
};

console.log(filterInt("421")); // 421
console.log(filterInt("-421")); // -421
console.log(filterInt("+421")); // 421
console.log(filterInt("Infinity")); // Infinity
console.log(filterInt("421e+0")); // NaN
console.log(filterInt("421hop")); // NaN
console.log(filterInt("hop1.61803398875")); // NaN
console.log(filterInt("1.61803398875")); // NaN

Specification
ECMAScript 2027 LanguageSpecification # sec-parseint-string-radix

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