The parseFloat()
function parses a string argument and returns a floating point number.
parseFloat(string)
string
parseFloat
is a top-level function and is not associated with any object.
parseFloat
parses its argument, a string, and returns a floating point number. If it encounters a character other than a sign (+ or -), numeral (0-9), a decimal point, or an exponent, it returns the value up to that point and ignores that character and all succeeding characters. Leading and trailing spaces are allowed.
If the first character cannot be converted to a number, parseFloat
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 parseFloat
is NaN
. If NaN
is passed on to arithmetic operations, the operation results will also be NaN
.
parseFloat
can also parse and return the value Infinity
. You can use the isFinite function to determine if the result is a finite number (not Infinity
, -Infinity
, or NaN
).
parseFloat
returning a numberThe following examples all return 3.14
parseFloat("3.14"); parseFloat("314e-2"); parseFloat("0.0314E+2"); parseFloat("3.14more non-digit characters");
parseFloat
returning NaNThe following example returns NaN
parseFloat("FF2");
It is sometime useful to have a stricter way to parse float values, regular expressions can help :
var filterFloat = function (value) { if(/^(\-|\+)?([0-9]+(\.[0-9]+)?|Infinity)$/ .test(value)) return Number(value); return NaN; } console.log(filterFloat('421')); // 421 console.log(filterFloat('-421')); // -421 console.log(filterFloat('+421')); // 421 console.log(filterFloat('Infinity')); // Infinity console.log(filterFloat('1.61803398875')); // 1.61803398875 console.log(filterFloat('421e+0')); // NaN console.log(filterFloat('421hop')); // NaN console.log(filterFloat('hop1.61803398875')); // NaN
Note that this code is an example only; it does not accept valid numbers such as 1.
or .5
.
Created by Mozilla Contributors, license: CC-BY-SA 2.5