Javascript parseFloat: Examples and variations of this function

We can use the parseFloat method to convert a string into a floating-point number. The parseFloat method takes a string value and returns a floating-point number. But there are few rules for using parseFloat method in JavaScript. We will discuss these rules of using parseFloat method in this article.

parseFloat parameters

In JavaScript, the parseFloat() function has only one parameter, which is the string that needs to be parsed and converted into a floating-point number. The parameter is passed as follows:

parseFloat(string)

The string parameter represents the input string that you want to parse. It should contain a representation of a number that you want to convert to a floating-point value. The function will attempt to extract the numeric portion from the string and convert it into a floating-point number.

Here’s an example that demonstrates the usage of parseFloat() with its parameter:

var numString = "3.14";
var floatNumber = parseFloat(numString);
console.log(floatNumber); // Output: 3.14

In the example above, the parseFloat() function is called with the numString variable as the parameter. The numString variable contains the string “3.14”, which represents a numeric value. The function parses the string and returns the floating-point number 3.14.

Basic usage of parseFloat in Javascript

In JavaScript, the parseFloat() function is used to convert a string representation of a number into a floating-point number. It parses the input string and returns a floating-point value based on the numeric portion of the string.

Here’s how the parseFloat() function works:

1. The parseFloat() function takes a single parameter, which is the string that needs to be converted to a floating-point number.
2. It starts parsing the string from the beginning until it encounters a character that is not a part of a valid numeric value. This can include digits (0-9), a decimal point (.), or certain special characters like a positive (+) or negative (-) sign.
3. The function ignores leading whitespace characters (spaces) before parsing the numeric value.
4. Once a non-numeric character is encountered or the end of the string is reached, parseFloat() stops parsing and returns the parsed floating-point number.
5. If the input string doesn’t contain a valid numeric value at the beginning, or if it cannot be converted to a number, parseFloat() returns NaN (Not a Number).
6. If the string contains a valid numeric value followed by non-numeric characters, parseFloat() ignores the non-numeric part and returns the parsed floating-point number.

Here’s an example that demonstrates the usage of parseFloat():

var numString = "3.14";
var floatNumber = parseFloat(numString);
console.log(floatNumber); // Output: 3.14

var invalidString = "abc123";
var invalidNumber = parseFloat(invalidString);
console.log(invalidNumber); // Output: NaN

In the example above, parseFloat() successfully converts the string “3.14” into the floating-point number 3.14. However, when parsing the string “abc123”, which contains non-numeric characters, parseFloat() returns NaN.

Examples of parseFloat in JavaScript

Let’s understand the parseFloat method in JavaScript with the help of a simple example.

Example 1

var result = parseFloat("100");

The output is:

In the above example, we used the parseFloat method and passed a string value. The string value equals 100. The parseFloat methods an integer value that equals 100. This is how the parseFloat method works in java. A string value containing numbers is passed and a corresponding integer is returned. But the parseFloat method only converts the first number of a string into an integer. Let’s understand this with the help of an example.

Example 2

var result = parseFloat("10 20 30");

The output is:

We pass the string value of “10 20 30” in the parseFloat method. But the value returned by the parseFloat method is only 10. This is because the first number in the string we pass is 10. After 10, there is whitespace. The parseFloat method does not count anything after whitespaces in the string. In fact, it does not count anything in the string after any non-number character. Observe the following example.

Example 3

var result = parseFloat("This is 10");

The output is:

We passed “This is 10” in the parseFloat function. Even there is a number in the string we passed but the output is NaN(Not a Number). This happens because the number in the string is after the alphabets. This is not allowed in parseFloat methods. But trailing and leading whitespaces are allowed in the parseFloat method. The same happens when a number in string is in front of non-number characters.

Example 4

var result = parseFloat("10 is a number");

The output is:

Example 5

var result = parseFloat("    100    ");

The output is:

We passed a string containing a number in the parseFloat method. But the string also contains trailing and leading whitespaces. Even because of the whitespaces, the value returned is 100. This is because the trailing and leading whitespaces are allowed in the parseFloat method.

We have to remember that if the first character of the string passed in the parseFloat method is not a number, the result will be NaN.

Using parseFloat with decimals

The parseFloat method in javascript can also be used with decimals. We can pass a string containing a decimal number and get the corresponding floating-point number. The following example shows a decimal number passed in a parseFloat method.

 var result = parseFloat("100.33445");

The output is:

In the above code, we pass “100.33445” to the parseFloat method. The returned value is exactly the same. This is how the parseFloat method works with decimals.

We can also fix the numbers after decimal the help of toFixed methods. We have to pass a number in the toFixed method and the resulting integer will have that many numbers of digits after the decimal. The following example shows how to use the toFixed method with the parseFloat.

 var result = parseFloat("100.334445").toFixed(2);

The output is:

In the above code, we use a toFixed method and passed a value of 2 in it. The string we passed in the parseFloat method has five digits after the decimal but the returned value has only two. This is because of the toFixed method. The value returned is always a round-off value. But what happens when no value is passed in the toFixed method?

var result = parseFloat("100.334445").toFixed();

The output is:

The value returned has no decimal when there no value passed in the toFixed method.

Using parseFloat with commas

Like other non-numbers, no character will be considered after a comma in the string passed in the parseFloat method. The only number in the string will be returned by the parseFloat method. The following is an example of parseFloat with a comma.

var result = parseFloat("10,12")

The output is:

In the above code, for example, we passed a string with a comma in the parseFloat method. The output is only the number before a comma.

Other usages

What is parseFloat to number in JavaScript?

In JavaScript, the parseFloat() function is basically used to convert a string to a floating-point number. It parses the provided string and returns a floating-point number representation of the numeric portion of the string.

On the other hand, the Number() constructor or the unary plus operator (+) can be used to convert a value, including strings, to a number of any type (integer, floating-point, or even special values like NaN or Infinity).

Here’s a comparison of parseFloat() and Number() in JavaScript:

1. parseFloat():
   • Specifically designed to parse and convert a string to a floating-point number.
   • Extracts the numeric portion from the beginning of the string until it encounters a non-numeric character or reaches the end of the string.
   • Ignores leading whitespace characters before parsing the numeric value.
   • Returns NaN if the string does not contain a valid numeric value at the beginning.
2. Number() or + operator:
   • More versatile and can convert values of various types to numbers.
   • Can convert strings, booleans, null, undefined, and other values to numbers.
   • Behaves differently based on the input type. For strings, it behaves similar to parseFloat(), but it can also convert other types to numbers.
   • Returns NaN if the conversion is not possible.

Here are examples demonstrating the difference between parseFloat() and Number():

var numString = "3.14";
var floatNumber = parseFloat(numString);
var number = Number(numString);

console.log(floatNumber); // Output: 3.14
console.log(number);      // Output: 3.14

In the example above, both parseFloat() and Number() are used to convert the string “3.14” to a number. The output for both cases is 3.14. However, Number() is more versatile and can handle conversions for various types, while parseFloat() is specifically designed for parsing strings to floating-point numbers.

How parseInt works in JavaScript?

In JavaScript, the parseInt() function is used to parse a string and convert it into an integer. It takes two parameters: the string to be parsed and an optional radix (base) indicating the numeric base for parsing. The parseInt() function follows these rules:

1. Parsing the String:
   • parseInt() starts parsing the string from the beginning until it encounters a non-numeric character or reaches the end of the string.
   • Leading whitespace characters are ignored.
   • The parsing stops when a non-numeric character is encountered, and the numeric portion of the string parsed up to that point is returned.
2. Radix (Base):
   • The second parameter, radix, is optional and specifies the base of the numeric system to use for parsing.
   • If the radix is not specified, parseInt() assumes a base 10 (decimal) system.
   • If the radix is specified, it must be an integer between 2 and 36.
   • The radix parameter is typically used when parsing strings representing numbers in different bases, such as binary (base 2), octal (base 8), or hexadecimal (base 16).

Here’s an example of parseInt() in action:

var number1 = parseInt("42");
console.log(number1); // Output: 42

var number2 = parseInt("1010", 2); // Parsing a binary string
console.log(number2); // Output: 10

In the example above, parseInt() is used to parse the strings “42” and “1010”. The first example uses the default base 10 (decimal), while the second example specifies a base of 2 (binary). The output for the first parseInt() call is 42, and for the second call, it is 10, representing the parsed integer value.

Should I use parseInt or parseFloat in JavaScript?

The choice between parseInt() and parseFloat() depends on the specific requirements of your code and the type of numeric value you need to extract from a string. Here are some factors to consider when deciding which function to use:

1. Integer vs. Floating-Point:
   • Use parseInt() when you specifically need to extract an integer value from a string. It will discard any fractional part and return an integer.
   • Use parseFloat() when you need to extract a floating-point number that may contain decimal places. It will preserve the fractional part and return a floating-point number.
2. Numeric Base:
   • If you are parsing strings representing numbers in different bases, such as binary, octal, or hexadecimal, you should use parseInt() with the appropriate radix (base) parameter. parseFloat() only works with decimal representations.
3. Handling Non-numeric Characters:
   • parseInt() and parseFloat() behave differently when encountering non-numeric characters in the string.
   • parseInt() stops parsing as soon as it encounters a non-numeric character and returns the parsed integer value up to that point.
   • parseFloat() continues parsing until it reaches the end of the string or encounters an invalid character, and it returns the parsed floating-point value up to that point.
4. Precision and Decimal Places:
   • If you need precise decimal calculations or need to preserve decimal places, you should use parseFloat(). JavaScript’s parseFloat() supports double-precision floating-point numbers, providing more precision than integers obtained from parseInt().

In general, if you’re dealing with decimal values, fractional parts, or non-integer numbers, parseFloat() is a more appropriate choice. However, if you specifically need to extract integers or parse numbers in different bases, parseInt() is the suitable option.

The history of parseFloat in JavaScript

The parseFloat() function has been a part of JavaScript since its early versions. It was introduced in the ECMAScript 1 (ES1) specification, which standardized the core features of the language, in 1997. Since then, parseFloat() has remained a fundamental function for parsing strings into floating-point numbers in JavaScript.

Since its initial introduction, parseFloat() has undergone minimal changes in terms of its behavior and usage. The function is designed to extract and convert the numeric portion of a string while preserving the decimal places.

The behavior of parseFloat() has been consistently defined and standardized across different ECMAScript specifications, ensuring consistent results across various JavaScript implementations.

One notable aspect of parseFloat() is its handling of leading whitespace characters, which are ignored during parsing. This behavior has remained consistent throughout the history of the function.

Overall, the parseFloat() function has a longstanding history in JavaScript and has been a reliable tool for parsing strings into floating-point numbers. Its behavior has remained relatively stable, providing consistent results for converting string representations of numeric values into floating-point numbers.

parseFloat in other programming languages

Basically, several programming languages have functions or methods similar to JavaScript’s parseFloat() for parsing strings into floating-point numbers. Some examples include:

• Python: Python provides the float() function, which can parse a string and return a floating-point number. It behaves similarly to parseFloat() in JavaScript.
• Java: Java offers the Float.parseFloat() method, which parses a string and returns a float value. It functions similarly to parseFloat() in JavaScript.
• C#: In C#, the float.Parse() method is used to convert a string representation of a number into a float value. It shares similarities with parseFloat() in JavaScript.
• Ruby: Ruby provides the Float() method, which can parse a string and return a floating-point number. It functions similarly to parseFloat() in JavaScript.
• PHP: PHP offers the floatval() function, which can parse a string and return a float value. It is comparable to parseFloat() in JavaScript.

It’s important to note that while these languages provide similar functionality for parsing strings into floating-point numbers, the exact behavior and usage of these functions/methods may have slight variations. It’s recommended to consult the respective language documentation for precise details on how to use these parsing functions in each language.

Conclusion

Javascript is a scripting language that provides many in-built functions that are very helpful while coding. The parseFloat is an in-built function used to parse any numbers in a string to a floating-point method. It is immensely useful while tracking numbers in a string. But there are few rules of using the parseFloat function that we discussed in this article.