Question

I’m having a problem when executing parseFloat() – I don’t understand why it produces the following outputs:

document.write(parseFloat("6e2") + "<br />"); //output is 600 why?
document.write(parseFloat("6b2") + "<br />"); //output is 6 why?
document.write(parseFloat("6c2") + "<br />"); //output is 6 why?

Could you tell me how the script is working?

Answer 1

6e2 produces 600 because it’s treating your input as scientific notation.

6e2 == 6 x 10² == 600

The other two produce 6 because parseFloat parses the 6, then gets to input it isn’t able to convert to a number, so it stops, and returns the result found so far.

Per MDN:

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.