parseInt()
function parses a string argument and returns an integer of the specified
radix
(the base in mathematical numeral systems).
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parseInt(string [, radix])
string
ToString
abstract operation. Leading
whitespace
in this argument is ignored.
radix
可选
2
and
36
that represents the
radix
(the base in mathematical numeral systems) of the
string
. Be careful—this does
not
default to
10
!
radix
is not provided.
An integer parsed from the given
string
.
Or
NaN
when
radix
<
2
or bigger than
36
，或
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.
若
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 × 10
23
), 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.
若
radix
is
undefined
,
0
, or unspecified, JavaScript assumes the following:
string
begins with "
0x
" or "
0X
" (a zero, followed by lowercase or uppercase X),
radix
is assumed to be
16
and the rest of the string is parsed as a hexidecimal number.
string
begins with "
0
" (a zero),
radix
is assumed to be
8
(octal) or
10
(decimal). Exactly which radix is chosen is implementation-dependent. ECMAScript 5 clarifies that
10
(decimal)
should
be used, but not all browsers support this yet. For this reason,
always specify a
radix
当使用
parseInt
.
string
begins with any other value, the radix is
10
(decimal).
If the first character cannot be converted to a number,
parseInt
返回
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
。若
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
警告：
parseInt
converts a
BigInt
到
Number
and loses precision in the process. This is because trailing non-numeric values, including "
n
", are discarded.
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:
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 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 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 .
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
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
| 规范 |
|---|
|
ECMAScript (ECMA-262)
The definition of 'parseInt' in that specification. |
| Desktop | Mobile | Server | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
parseInt
|
Chrome 1 | Edge 12 | Firefox 1 | IE 3 | Opera 3 | Safari 1 | WebView Android 1 | Chrome Android 18 | Firefox Android 4 | Opera Android 10.1 | Safari iOS 1 | Samsung Internet Android 1.0 | nodejs 0.1.100 |
| Parses leading-zero strings are decimal, not octal | Chrome 23 | Edge 12 | Firefox 21 | IE 9 | Opera 15 | Safari 6 | WebView Android 4.4 | Chrome Android 25 | Firefox Android 21 | Opera Android 14 | Safari iOS 6 | Samsung Internet Android 1.5 | nodejs 0.10 |
完整支持