parseFloat()
function parses an argument (converting it to a string first if needed) and returns a floating point number.
parseFloat(string)
string
ToString
abstract operation. Leading
whitespace
in this argument is ignored.
A floating point number parsed from the given
string
.
Or
NaN
when the first non-whitespace character cannot be converted to a number.
parseFloat
is a top-level function and not a method of any object.
parseFloat
encounters a character other than a plus sign (
+
), minus sign (
-
U+002D HYPHEN-MINUS), numeral (
0
–
9
), decimal point (
.
), or exponent (
e
or
E
), it returns the value up to that character, ignoring the invalid character and characters following it.
parseFloat
返回
NaN
.
parseFloat
can also parse and return
Infinity
.
parseFloat
converts
BigInt
syntax to
数字
, losing precision. This happens because the trailing
n
character is discarded.
Consider
Number(value)
for stricter parsing, which converts to
NaN
for arguments with invalid characters anywhere.
parseFloat
will parse non-string objects if they have a
toString
or
valueOf
method. The returned value is the same as if
parseFloat
had been called on the result of those methods.
parseFloat
returning a number
The following examples all return
3.14
:
parseFloat(3.14);
parseFloat('3.14');
parseFloat(' 3.14 ');
parseFloat('314e-2');
parseFloat('0.0314E+2');
parseFloat('3.14some non-digit characters');
parseFloat({ toString: function() { return "3.14" } });
parseFloat
returning
NaN
The following example returns
NaN
:
parseFloat('FF2');
parseFloat
and
BigInt
The following examples both return
900719925474099300
, losing precision as the integer is too large to be represented as a float:
parseFloat(900719925474099267n);
parseFloat('900719925474099267n');
| 规范 |
|---|
|
ECMAScript (ECMA-262)
The definition of 'parseFloat' in that specification. |
| Desktop | Mobile | Server | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
parseFloat
|
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 |
完整支持