[Chapter 21] Reference: parseFloat()
Author: David Flanagan
Date: Fri Aug 29 11:18:52 1997

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| Chapter 21 JavaScript Reference |

# parseFloat() Function

## Name

parseFloat() Function---convert a string to a number

## Availability

Navigator 3.0, partial support in Navigator 2.0 and Internet Explorer 3.0

## Synopsis

    parseFloat(s)

### Arguments

`s`

  The string to be parsed and converted to a number.

### Returns

The parsed number, or `NaN`, if `s` does not begin with a valid number. Because Navigator 2.0 and Internet Explorer 3.0 do not support `NaN`, those browsers return 0 when `s` cannot be parsed.

## Description

`parseFloat()` is a built-in function in JavaScript; it is a core part of the language, and is not a method of any object.

`parseFloat()` parses and returns the first number that occurs in `s.` Parsing stops, and the value returned, when `parseFloat()` encounters a character in `s` that is not a valid part of the number (i.e., a sign, a digit, decimal point, exponent, etc.) If `s` does not begin with a number that `parseFloat()` can parse, then the function returns `NaN`, a reserved value that represents "not-a-number". You can test for the `NaN` value with the `isNaN()` function. If `NaN` is used with arithmetic operations, the result will always be `NaN.` In Navigator 2.0 (except Unix platforms) and Internet Explorer 3.0, `parseFloat()` returns 0 instead of `NaN` when the input cannot be parsed.

## Bugs

In Navigator 2.0 (except Unix platforms) and Internet Explorer 3.0, the `NaN` return value is not implemented, and so `parseFloat()` returns 0 when it cannot parse a number. When you receive this return value on those platforms, you must perform additional tests to determine whether the string contains illegal input or actually contains the value 0.

## See Also

"isNaN()", "parseInt()"

parent |  | parseInt()