The num.toExponential([fractionDigits]) method in JavaScript is used to convert a number into a string representation in exponential (scientific) notation. This is particularly useful for representing very large or very small numbers in a more compact form.

Syntax:

num.toExponential([fractionDigits])

• num: The number you want to convert to exponential notation.
• fractionDigits (optional): A number specifying the number of digits after the decimal point in the resulting string. This value must be between 0 and 20. If omitted, JavaScript will use as many digits as necessary to represent the number accurately.

Return Value:

• Returns a string representing the number in exponential notation, formatted as x.yyyy...e+/-z, where:
  • x is a non-zero digit,
  • y represents the digits after the decimal point,
  • e indicates "times ten raised to the power of",
  • z is the exponent.

Example Usage:

1. Basic Usage:

   let num1 = 123456;
   console.log(num1.toExponential()); // "1.23456e+5"
   

2. Specifying Fraction Digits:

   let num2 = 0.000123456;
   console.log(num2.toExponential(3)); // "1.235e-4"
   console.log(num2.toExponential(5)); // "1.23456e-4"
   

3. Using with Large Numbers:

   let num3 = 9876543210;
   console.log(num3.toExponential(2)); // "9.88e+9"
   

4. Using with Small Numbers:

   let num4 = 0.000000000123;
   console.log(num4.toExponential(2)); // "1.23e-10"
   

5. Omitting Fraction Digits:

   let num5 = 2.5e-3;
   console.log(num5.toExponential()); // "2.5e-3"
   

Notes:

• If the fractionDigits argument is outside the valid range (0-20), a RangeError will be thrown.
• If num is NaN, Infinity, or -Infinity, the method will return the string representation of these values ("NaN" or "Infinity").

Summary:

The num.toExponential([fractionDigits]) method is a convenient way to represent numbers in exponential notation in JavaScript. It allows for precise control over the formatting of decimal places, making it easier to work with very large or very small values.