[JS] Data Types - Numbers

Contents

• 1. Ways to Write Numbers
• 2. toString(base)
• 3. Rounding
• 4. Imprecise Calculations
• 5. parseInt and parseFloat
• 6. Other Math Functions

1. Ways to Write Numbers

• Different ways to write 1 billion.

let billion = 1000000000;
let billion = 1_000_000_000;
let billion = 1e9;

• Different ways to write 0.001.

let num = 0.001;
let num = 1e-3;

2. toString(base)

• Returns a string representation of a number

• Two dots to call a method.

  • If we want to call a method directly on a number, use two dots.

  123..toString()
  

  • JavaScript syntax implies the decimal part after the first dot.

  • We can also use

  (123).toString()
  

3. Rounding

• Math.floor

  • Rounds down: 3.1 becomes 3, and -1.1 becomes -2.

• Math.ceil

  • Rounds up: 3.1 becomes 4, and -1.1 becomes -1.

• Math.round

  • Rounds to the nearest integer: 3.1 becomes 3, and 3.5 becomes 4.

• Math.trunc

  • Removes anything after the decimal point: 3.1 becomes 3.

• Round to n-th digit

  1. Multiply-and-divide

     let num = 1.23456;
     
     console.log(Math.round(num * 100) / 100); // 1.23
     

  2. toFixed(n): round numbers to ndigits after point and returns a string

     let num = 12.36;
     
     console.log(num.toFixed(1)); // "12.4"
     
     let num2 = 12.34;
     
     console.log(num.toFixed(5)); // "12.34000" zeroes added to match exactly 5
     

4. Imprecise Calculations

console.log(0.1 + 0.2 == 0.3); // false

console.log(0.1 + 0.2); // 0.30000000000000004

This example returns false because there is no way to store exactly 0.1 or 0.2. The most reliable way to solve this problem is to use the method toFixed(n). Remember that toFixed(n) returns a string. We can use the unary plus to coerce it into a number.

let sum = 0.1 + 0.2;

console.log(+sum.toFixed(2)); // 0.3

5. parseInt and parseFloat

Numeric conversion using + and Number is strict. It only accepts a values that is exactly a number. For example, this won’t work since it has a string in it.

console.log(+"100px"); // NaN

To solve this kind of error, we can use parseInt and parseFloat. They read a number from a string until they can’t.

• parseInt: returns an integer
  • Second Parameter: specifies the base of numeral system.
• parseFloat: returns a float

alert(parseInt("100px")); // 100
alert(parseFloat("12.5em")); // 12.5

alert(parseInt("12.3")); // 12, only the integer part is returned
alert(parseFloat("12.3.4")); // 12.3, the second point stops the reading

6. Other Math Functions

• Math.random()

  • Returns a random number from 0 to 1 (not including 1).

  alert(Math.random()); // 0.1234567894322
  alert(Math.random()); // 0.5435252343232
  

• Math.max() & Math.min()

  • Returns the max and min number.

  alert(Math.max(3, 5, -10, 0, 1)); // 5
  alert(Math.min(1, 2)); // 1
  

• Math.pow(n, power)

  • Returns n raised to the given power.

    alert(Math.pow(2, 10)); // 2 in power 10 = 1024