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The parseInt()
function parses a string argument and returns an integer of the specified radix (the base in mathematical numeral systems).
Syntax
parseInt(string, radix);
Parameters
string
- The value to parse. If the
string
argument is not a string, then it is converted to a string (using theToString
abstract operation). Leading whitespace in the string argument is ignored. radix
- An integer between 2 and 36 that represents the radix (the base in mathematical numeral systems) of the above mentioned string. Specify
10
for the decimal numeral system commonly used by humans. Always specify this parameter to eliminate reader confusion and to guarantee predictable behavior. Different implementations produce different results when a radix is not specified, usually defaulting the value to 10.
Return value
An integer number parsed from the given string. If the first character cannot be converted to a number, NaN
is returned.
Description
The parseInt
function converts its first argument to a string, parses it, and returns an integer or NaN
. If not NaN
, the returned value will be the integer that is the first argument taken as a number in the specified radix (base). For example, a radix of 10 indicates to convert from a decimal number, 8 octal, 16 hexadecimal, and so on. 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.
If parseInt
encounters a character that is not a numeral in the specified radix, it ignores it and all succeeding characters and returns the integer value parsed up to that point. parseInt
truncates numbers to integer values. Leading and trailing spaces are allowed.
If radix is undefined
or 0 (or absent), JavaScript assumes the following:
- If the input
string
begins with "0x" or "0X", radix is 16 (hexadecimal) and the remainder of the string is parsed. - If the input
string
begins with "0", radix is eight (octal) or 10 (decimal). Exactly which radix is chosen is implementation-dependent. ECMAScript 5 specifies that 10 (decimal) is used, but not all browsers support this yet. For this reason always specify a radix when usingparseInt
. - If the input
string
begins with any other value, the radix is 10 (decimal).
If the first character cannot be converted to a number, parseInt
returns 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
.
To convert number to its string literal in a particular radix use intValue.toString(radix)
.
Examples
Using parseInt
The following examples all return 15
:
parseInt(" 0xF", 16); parseInt(" F", 16); parseInt("17", 8); parseInt(021, 8); parseInt("015", 10); // parseInt(015, 10); will return 13 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);
The following examples all return NaN
:
parseInt("Hello", 8); // Not a number at all parseInt("546", 2); // Digits are not valid for binary representations
The following examples all return -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);
The following example returns 224
:
parseInt("0e0", 16);
Octal interpretations with no radix
Although discouraged by ECMAScript 3 and forbidden by ECMAScript 5, many implementations interpret a numeric string beginning with a leading 0
as octal. The following may have an octal result, or it may have a decimal result. Always specify a radix to avoid this unreliable behavior.
parseInt("0e0"); // 0 parseInt("08"); // 0, '8' is not an octal digit.
ECMAScript 5 removes 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.
A stricter parse function
It is sometimes useful to have a stricter way to parse int values. Regular expressions can help:
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
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. |
ECMAScript 5.1 (ECMA-262) The definition of 'parseInt' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'parseInt' in that specification. |
Standard | |
ECMAScript 2017 Draft (ECMA-262) The definition of 'parseInt' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | ? | (Yes) |
Parses leading-zero strings as decimal, not octal | (Yes) | 21 | (Yes) (in standards mode) | ? | (Yes) |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) | (Yes) |
Parses leading-zero strings as decimal, not octal | ? | ? | 21 | ? | ? | ? |