1. Converting a String to a number

JavaScript provides the following methods to convert strings to numbers

  1. Number(): This method converts the given argument to a number.
  2. parseInt(): Converts the given string to an integer.
  3. parseFloat(): Returns the floating-point number after parsing the given string. 

Example:

var num = '10.25';
console.log(Number(num));
console.log(parseInt(num));
console.log(parseFloat(num));

Output:

10.25

10

10.25

2. Creating a number object

You can also create an object whose data type is a number using the Number() costructor.

Example:

var num = new Number(45);
console.log(num);
console.log(typeof num.valueOf());

Output:

Number { 45 }

number

3. Checking if a value is a number or not

isNaN() can be used to check if a value is a number or not. "NaN stands for Not a Number". isNaN() returns false if a value is a number and true if a value is not a number.

Example:

var num1 = new Number(45);
var num2 = new Number('abc');
console.log(isNaN(num1));
console.log(isNaN(num2));

Output:

false

true

4. Fixing the number of digits

toPrecision() and toFixed() methods are used to fix the number of digits in a number.

toPrecision(): will limit the total number of digits in a number.

toFixed(): will limit the total number of digits that appear after the decimal point in a floating-point number.

Example:

var num1 = 23.347389
console.log(num1.toPrecision());
console.log(num1.toPrecision(5));
console.log(num1.toFixed(5))

Output:

23.347389
23.347
23.34739

Note: toFixed() performs the rounding off operation to shorten the number as you can see in the example above.

5. Absolute value of a number

Math.abs() is used to find the absolute value of a number in javascript.

Example:

console.log(Math.abs());
console.log(Math.abs(-5));

Output:

NaN
5

6. Finding the maximum number

Math.max() returns the maximum number of the provided numbers.

Example:

console.log(Math.max(1, -20));
console.log(Math.max(40, 50, 20, -8, 109));

Output:

1
109

7. Square root of a number

Math.sqrt() returns the square root of the given argument.

Example:

console.log(Math.sqrt(9));
console.log(Math.sqrt('abc'));

Output:

3
NaN

8. Floor and Ceil 

Math.floor() rounds off the number to the closest lowest integer.

Math.ceil() rounds off the number to the closest highest integer.

Example:

console.log(Math.floor(9.4));
console.log(Math.ceil(9.4));

Output:

9
10

9. Length of a number

Unlike strings, there is no method to find the length of a number in javascript. However, you can write your own code to find the length of a number.

Example:

var num = 8389457834;
var len = Math.log(num) * Math.LOG10E + 1 | 0;
console.log(len);

Output:

10

10. Swapping two numbers

This is one of the common questions which are repeatedly asked in an interview.

10.1. Using a temporary variable

You can swap the value of two variables using a third temporary variable by exchanging their values one by one.

Example:

var num1 = 45;
var num2 = 90;
console.log("Before Swapping num1 : " +num1+" num2 : "+num2);
var temp;
temp = num1;
num1 = num2;
num2 = temp;
console.log("After swapping num1 : " +num1+" num2 : "+num2);

Output:

Before Swapping num1 : 45 num2 : 90

After swapping num1 : 90 num2 : 45

10.2. Without temporary variable

You can also swap values of two variables without a temporary variable.

Example:

var num1 = 45;
var num2 = 90;
console.log("Before Swapping num1 : " +num1+" num2 : "+num2);
num2 = num2 - num1;
num1 = num1 + num2;
num2 = num1 - num2;
console.log("After swapping num1 : " +num1+" num2 : "+num2);

Output:

Before Swapping num1 : 45 num2 : 90

After swapping num1 : 90 num2 : 45

11. Conclusion

There are a lot of methods you can use in javascript while working with numbers in javascript which makes using numbers in javascript quite easy.