parseFloat() function parses a string argument and returns a floating point number.
- : The value to parse, coerced to a string. Leading whitespace in this argument is ignored.
A floating point number parsed from the given
NaN when the first non-whitespace character cannot be converted to a number.
parseFloat()only differ in their parsing behavior, but not necessarily their return values. For example,
parseFloat("42")would return the same value: a
parseFloat function converts its first argument to a string, parses that string as a decimal number literal, then returns a number or
NaN. The number syntax it accepts can be summarized as:
- The characters accepted by
parseFloat()are plus sign (
+), minus sign (
-U+002D HYPHEN-MINUS), decimal digits (
9), decimal point (
.), exponent indicator (
E), and the
-signs can only appear strictly at the beginning of the string, or immediately following the
Echaracter. The decimal point can only appear once, and only before the
Echaracter can only appear once, and only if there is at least one digit before it.
- Leading spaces in the argument are trimmed and ignored.
parseFloat()can also parse and return
-Infinityif the string starts with
"-Infinity"preceded by none or more white spaces.
parseFloat()picks the longest substring starting from the beginning that generates a valid number literal. If it encounters an invalid character, it returns the number represented up to that point, ignoring the invalid character and all characters following it.
- If the argument's first character can't start a legal number literal per the syntax above,
parseFloat() parses a subset of the syntax that the
Number() function accepts. Namely,
parseFloat() does not support non-decimal literals with
0o prefixes but supports everything else. However,
parseFloat() is more lenient than
Number() because it ignores trailing invalid characters, which would cause
Number() to return
Similar to number literals and
Number(), the number returned from
parseFloat() may not be exactly equal to the number represented by the string, due to floating point range and inaccuracy. For numbers outside the
1.7976931348623158e+308 range (see
Infinity is returned.