JavaScript Number parseFloat() Method

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The JavaScript Number parseFloat() method is used for converting a string argument into a floating-point number. If the string does not start with a valid number, or if the first character of the passed string cannot be converted, "NaN" is returned. It ignores any leading or trailing white spaces before and after the string.

Note: To parse a string means to understand it in a certain way. For example, parsing the string "10" as a number means understanding it as the number ten.

What is Floating Point Number ?

A floating point number, is a positive or negative whole number with a decimal point. For example, 1.2, 2.3, 4.5, ...etc.

Syntax

Following is the syntax of JavaScript Number parseFloat() method −

parseFloat(string)

Parameters

This method accepts a parameter named 'string'. The same is described below −

  • string − The value to be parsed.

Return value

This method returns a floating point number from the given string, 'NaN' if the first non-white space character can't be converted to a number.

Example 1

The following example demonstrates the usage of the Number parseFloat() method.

<html>
<head>
<title>JavaScript parseFloat() Method</title>
</head>
<body>
<script>
   let val = "10.23Ab";
   document.write("Given value= " , val)
   document.write("<br>Floating-point number = ", Number.parseFloat(val));
</script>
</body>
</html>

Output

The program mentioned above returns the floating-point number "10.23" as shown below −

Given value= 10.23Ab
Floating-point number = 10.23

Example 2

If the value passed to this method is not valid, it will return 'NaN'.

In the following program, we are using the parseFloat() method to retrieve a floating-point number from the passed value 'ABC'.

<html>
<head>
<title>JavaScript parseFloat() Method</title>
</head>
<body>
<script>
   let val = "ABC";
   document.write("Given value= " , val)
   document.write("
Floating-point number = ", Number.parseFloat(val));
</script>
</body>
</html>

Output

The above program returns 'NaN' for invalid values as −

Given value= ABC
Floating-point number = NaN

Example 3

If we pass NaN as an argument to this method, it will return 'NaN' as the output.

Here is an example of the JavaScript Number parseFloat() method. If we pass the string 'NaN' to this method, which is an invalid syntax accepted by the method, it will return 'NaN'.

<html>
<head>
<title>JavaScript parseFloat() Method</title>
</head>
<body>
<script>
   let val = "NaN";
   document.write("Given value= " , val)
   document.write("<br>Floating-point number = ", Number.parseFloat(val));
</script>
</body>
</html>

Output

After executing the above program, it will return 'NaN' in the output −

Given value= NaN
Floating-point number = NaN

Example 4

In the following program, the parseFloat() method takes "1.7976931348623159e+308" as an argument and returns "Infinity" in the output.

<html>
<head>
<title>JavaScript parseFloat() Method</title>
</head>
<body>
<script>
   let val = "1.7976931348623159e+308";
   document.write("Given value = " , val)
   document.write("<br>Floating-point number = ", Number.parseFloat(val));
</script>
</body>
</html>

Output

The above program returns "Infinity" for the large values like "1.7976931348623159e+308".

Given value = 1.7976931348623159e+308
Floating-point number = Infinity

Example 5

Let's see what happens if the first character of the given string is Not valid.

<html>
<head>
<title>JavaScript parseFloat() Method</title>
</head>
<body>
<script>
   let val = "a1234";
   document.write("Given value= " , val)
   document.write("
Floating-point number = ", Number.parseFloat(val));
</script>
</body>
</html>

Output

If the first character of the given string is invalid, the parseFloat() method returns 'NaN' as shown below −

Given value= a1234
Floating-point number = NaN
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