What are Datatypes?
We use datatypes to store a specific value in a so called variable or whatever…
Data can be divided into two:
- primitive datatypes
- non-primitive datatypes
# Primitive
can be compared - TRUE/FALSE
| primitive type | datatype |
|---|---|
| Numbers | Integers, Floats |
| Strings | any data under ’ ’ or ” ” or `` |
| Booleans | true or false value |
| Null | no value or empty value |
| Undefined | declared variable without value |
| Symbol | unique value - can be created by Symbol constructor |
# Non-Primitive
can’t be compared - FALSE
| non-primitive type |
|---|
| Objects |
| Arrays |
| Functions |
let nums = [1, 2, 3]
nums[0] = 10
console.log(nums) // [10, 2, 3]# Numbers
represents integers & decimal values
# Math Object
provides lots of methods to work with numbers
const PI = Math.PI; // variable for PI(3.1415...)
console.log(Math.round(PI)); // 3 - rounds down
console.log(Math.round(9.81)) // 10 - rounds up
console.log(Math.floor(PI)) // 3 - rounds down
console.log(Math.ceil(PI)) // 4 - rounds up
console.log(Math.min(-5, 3, 20, 4, 5, 10)) // -5, returns the minimum value
console.log(Math.max(-5, 3, 20, 4, 5, 10)) // 20, returns the maximum value
const randNum = Math.random() * 11 // creates random number between 0 to 10
//Absolute value
console.log(Math.abs(-10)) // 10
//Square root
console.log(Math.sqrt(100)) // 10
// Power
console.log(Math.pow(3, 2)) // 9
console.log(Math.E) // 2.718
// Logarithm
// Returns the natural logarithm with base E of x, Math.log(x)
console.log(Math.log(2)) // 0.6931471805599453
console.log(Math.log(10)) // 2.302585092994046
// Returns the natural logarithm of 2 and 10 respectively
console.log(Math.LN2) // 0.6931471805599453
console.log(Math.LN10) // 2.302585092994046
// Trigonometry
Math.sin(60)
Math.cos(60)# Strings
represent text
- for declaring we need
" ", ' ', ``
// 2 back-ticks for template strings
console.log(`hello ${randomNum}`)
// else - interpreted as basic string
console.log("hello ${randomNum}")# String Methods
Each character in a string can be accessed by using its index. Every Index starts with 0 - ends with length of string -1
let string2 = 'I love JavaScript. If you do not love JavaScript what else can you love.'
let string1 = 'JavaScript'
let string = ' 30 Days Of JavaScript '
console.log(string1.length) // length of string - 9
console.log(string1.toUpperCase()) // JAVASCRIPT
console.log(string1.toLowerCase()) // javascript
console.log(string1.substr(4,6)) // Script
console.log(string1.substring(3)) // aScript
console.log(string.split()) // Changes to an array -> ["30 Days Of JavaScript"]
console.log(string.split(' ')) // Split to an array at space -> ["30", "Days", "Of", "JavaScript"]
console.log(string.trim(' ')) // "30 Days Of JavaScript"
console.log(string.includes('Days')) // true
console.log(string.includes('days')) // false - it is case sensitive!
console.log(string.replace('JavaScript', 'C#')) // 30 Days Of C#
console.log(string.charAt(0)) // 3
console.log(string.charCodeAt(3)) // D ASCII number is 68
console.log(string.indexOf('D')) // 3
console.log(string2.lastIndexOf('JavaScript')) // 38
let string3 = '30'
console.log(string3.concat("Days", "Of", "JavaScript")) // 30DaysOfJavaScript
console.log(string2.startsWith('I')) // true
console.log(string2.endsWith('love.')) // true
console.log(string2.search('love')) // 2
let string4 = 'love'
console.log(string4.repeat(10)) // lovelovelovelovelovelovelovelovelovelove
let hello = 'hello123world456'
console.log(hello.match(/\d)) // "1"
console.log(hello.match(/\d/g)) // "1", "2", "3", "4", "5", "6"# Checking data types & Casting
# Check data types
To check data types, we use typeof method.
let test = 'sample' // string
let age = 250 // number
let job // undefined
console.log(typeof(test)) // string
console.log(typeof(age)) // number
console.log(typeof(job)) // undefined
console.log(typeof null) // object# Casting
Convert one data type to another
We use parseInt(), parseFloat(), Number()
// String --> Int
let num = '10'
let numInt = parseInt(num)
console.log(numInt) // 10
let numInt1 = Number(num)
console.log(numInt1) // 10
let numInt2 = +num
console.log(numInt2) // 10
// String --> Float
let num1 = '9.81'
let numFloat = parseFloat(num1)
... Number(...)
... = + ...
// Float --> Int
let num2 = 9.81
let numInt = parseInt(num2)
console.log(numInt) // 9