The parseInt()
function parses a string argument and returns an integer of the specified radix (the base in mathematical numeral systems).
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Syntax
parseInt(string [, radix])
Parameters
string
- The value to parse. If this argument is not a string, then it is converted to one using the
ToString
abstract operation. Leading whitespace in this argument is ignored. radix
Optional- An integer between
2
and36
that represents the radix (the base in mathematical numeral systems) of thestring
. Be careful—this does not default to10
! - The description below explains in more detail what happens when
radix
is not provided.
Return value
An integer parsed from the given string
.
Or NaN
when
- the
radix
is smaller than2
or bigger than36
, or - the first non-whitespace character cannot be converted to a number.
Description
The parseInt
function converts its first argument to a string, parses that string, then returns an integer or NaN
.
If not NaN
, the return value will be the integer that is the first argument taken as a number in the specified radix
. (For example, a radix
of 10
converts from a decimal number, 8
converts from octal, 16
from hexadecimal, and so on.)
For radices above 10
, letters of the English 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.
Because some numbers use the e
character in their string representation (e.g. 6.022e23
for 6.022 × 1023), using parseInt
to truncate numbers will produce unexpected results when used on very large or very small numbers. parseInt
should not be used as a substitute for Math.floor()
.
parseInt
understands exactly two signs: +
for positive, and -
for negative (since ECMAScript 1). It is done as an initial step in the parsing after whitespace is removed. If no signs are found, the algorithm moves to the following step; otherwise, it removes the sign and runs the number-parsing on the rest of the string.
If radix
is undefined
, 0
, or unspecified, JavaScript assumes the following:
- If the input
string
begins with "0x
" or "0X
" (a zero, followed by lowercase or uppercase X),radix
is assumed to be16
and the rest of the string is parsed as a hexidecimal number. - If the input
string
begins with "0
" (a zero),radix
is assumed to be8
(octal) or10
(decimal). Exactly which radix is chosen is implementation-dependent. ECMAScript 5 clarifies that10
(decimal) should be used, but not all browsers support this yet. For this reason, always specify aradix
when usingparseInt
. - If the input
string
begins with any other value, the radix is10
(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 result will also be NaN
.
To convert a number to its string literal in a particular radix, use thatNumber.toString(radix)
.
BigInt
Warning: parseInt
converts a BigInt
to a Number
and loses precision in the process. This is because trailing non-numeric values, including "n
", are discarded.
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, because '8' is not an octal digit.
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 whitespace in string is ignored. If radix isundefined
or0
, it is assumed to be10
except when the number begins with the character pairs0x
or0X
, in which case a radix of16
is assumed.
This differs from ECMAScript 3, which merely 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 integers.
Regular expressions can help:
function filterInt(value) { if (/^[-+]?(\d+|Infinity)$/.test(value)) { return Number(value) } else { 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
Examples
Using parseInt
The following examples all return 15
:
parseInt('0xF', 16) parseInt('F', 16) parseInt('17', 8) parseInt(021, 8) parseInt('015', 10) // but `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 other than 0 or 1 are invalid for binary radix
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 examples all return 4
.
parseInt(4.7, 10) parseInt(4.7 * 1e22, 10) // Very large number becomes 4 parseInt(0.00000000000434, 10) // Very small number becomes 4
If the number is greater than 1e+21 (including) or less than 1e-7 (including), it will return 1
. (when using radix 10).
parseInt(0.0000001,10); parseInt(0.000000123,10); parseInt(1e-7,10); parseInt(1000000000000000000000,10); parseInt(123000000000000000000000,10); parseInt(1e+21,10);
The following example returns 224
:
parseInt('0e0', 16)
BigInt
values lose precision:
parseInt('900719925474099267n') // 900719925474099300
parseInt
doesn't work with numeric separators:
parseInt('123_456') // 123
Specifications
Specification |
---|
ECMAScript (ECMA-262) The definition of 'parseInt' in that specification. |
Browser compatibility
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
parseInt | Chrome Full support 1 | Edge Full support 12 | Firefox Full support 1 | IE Full support 3 | Opera Full support 3 | Safari Full support 1 | WebView Android Full support 1 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 10.1 | Safari iOS Full support 1 | Samsung Internet Android Full support 1.0 | nodejs Full support 0.1.100 |
Parses leading-zero strings are decimal, not octal | Chrome Full support 23 | Edge Full support 12 | Firefox Full support 21 | IE Full support 9 | Opera Full support 15 | Safari Full support 6 | WebView Android Full support 4.4 | Chrome Android Full support 25 | Firefox Android Full support 21 | Opera Android Full support 14 | Safari iOS Full support 6 | Samsung Internet Android Full support 1.5 | nodejs Full support 0.10 |
Legend
- Full support
- Full support