Run Down a Number in JavaScript

Sometimes we might come across situations where we need to round off a number in JavaScript to a specific number of digits after the decimal point. This process is called "run down". There are several ways to do this in JavaScript. Let's take a look at some of them.

Using Math.floor()

One way to run down a number in JavaScript is by using the Math.floor() method. This method rounds down a number to the nearest integer. We can use this method in combination with the toFixed() method to run down a number to a specific number of decimal places.

let number = 3.14159;
let result = Math.floor(number * 100) / 100;
console.log(result.toFixed(2)); // Output: 3.14

In the above example, we first multiply the number by 100 and then use the Math.floor() method to round it down to the nearest integer. We then divide the result by 100 to get the number back to its original value but with only two decimal places. Finally, we use the toFixed() method to format the number to two decimal places.

Using Math.trunc()

Another way to run down a number in JavaScript is by using the Math.trunc() method. This method simply truncates a number to its integer part. We can use this method in combination with the toFixed() method to run down a number to a specific number of decimal places.

let number = 3.14159;
let result = Math.trunc(number * 100) / 100;
console.log(result.toFixed(2)); // Output: 3.14

In the above example, we first multiply the number by 100 and then use the Math.trunc() method to truncate it to its integer part. We then divide the result by 100 to get the number back to its original value but with only two decimal places. Finally, we use the toFixed() method to format the number to two decimal places.

Using parseFloat() and toFixed()

We can also run down a number in JavaScript by using the parseFloat() method along with the toFixed() method. The parseFloat() method parses a string argument and returns a floating-point number. We can use this method to turn a number into a string with a certain number of decimal places, and then use the toFixed() method to format it to the desired number of decimal places.

let number = 3.14159;
let result = parseFloat(number.toFixed(2));
console.log(result.toFixed(2)); // Output: 3.14

In the above example, we first use the toFixed() method to format the number to two decimal places and then use the parseFloat() method to turn it back into a floating-point number. Finally, we use the toFixed() method again to format it to two decimal places.

Conclusion

There are several ways to run down a number in JavaScript, each with its own advantages and disadvantages. We can use the Math.floor() method, Math.trunc() method, parseFloat() method, and toFixed() method to achieve this.