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🎄 Day 16 - JavaScript basics

🎄 Day 16 - JavaScript basics

by Nino · 81 things on Twos

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Creating Variables
JavaScript has variables
like moving boxes, variables have content and names that tell us what's inside
every variable needs a name
variable names need to be single words and, therefore, have no spaces
to help us understand what's inside a variable we pick descriptive names
const windyCity
variable names can contain numbers, too
adding numbers is useful with multiple similar variables
const car1
we use the = sign to store a value inside it
strings are words in double quotes
const city = "Chicago";
strings can contain all sorts of letters and symbols, including spaces
"Winter is coming."
we use const to declare variables whose values are not supposed to change. const is short for "constant"
const age = 90; age = 91; // TypeError: Assignment to constant variable.
let age = 90; age = 91;
to make it obvious that a variable is of type const and shouldn't change, we can optionally name it with uppercase letters
const BIRTHDAY = "25/02/1882";
const SPEED_OF_LIGHT = "3*10⁸ m/s";
const MIDDLE_NAME = "Francesca";
with the special instruction console.log(), we tell the computer to display a value in an area called the console
console.log("Hello, world!");
we can also use console.log() to display variables like greeting
const greeting = "Hello, World!"; console.log(greeting); // Hello, World!
console is an area that displays output
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Using Variables
we can update let variables as often as we want
let currentStatus = "Watching Netflix"; currentStatus = "Relaxing at the beach"; console.log(currentStatus); // Relaxing at the beach
we can also give variables the values of other variables by setting one variable to the other
let defaultStatus = "Hi there!"; let currentStatus = "Playing football"; currentStatus = defaultStatus; console.log(currentStatus); // Hi there!
we call adding together string values an expression because it creates a single string value
const followers = "55"; "Followers:" + followers; // Followers:55
const numberOfFollowers = "55"; console.log("Followers:" + numberOfFollowers); // Followers:55
const title = "Ms. "; const name = "Irene"; console.log(title + name); // Ms. Irene
const numberOfLikes = "40 "; console.log(numberOfLikes + "likes"); // 40 likes
there are other kinds of values, too. Like numbers, which have no double quotes around them
numbers make it easier to keep track of numeric values.
const numberOfLikes = 5 + 1; console.log(numberOfLikes); // 6
const private = 3; const public = 10; const total = private + public; console.log("Total posts: " + total); // Total posts: 13
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Using True and False
there's a special value that's neither a string nor a number: true there are no quotes around it, and it's not a numeric value
true and false are great for situations like checking if a switch is on or if a feature is enabled.
they show if a feature is switched on or off
a ! sign in front of true makes the expression result in false
if something is not true, it has to be false
the ! sign is the negation operator. It turns values into their opposite
console.log(!true); // false
const isMorning = true; console.log(!isMorning); // false
const isMorning = true; const isEvening = !isMorning; console.log(isEvening); // false
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Checking Number Equality
we need to compare numbers in situations like checking a user's entered PIN matches their saved PIN
to compare if two numbers are the same, we use the equality operator, ===
when comparing, there are only two results: true or false
console.log(10 === 10); // true
const votes = 10; console.log(votes === 11); // false
to check if a number isn't equal to another number, we use the inequality operator, !==
console.log(1 !== 0); // true
we can store the result of a comparison with the inequality operator in a variable
const result = 1 !== 2; console.log(result); // true
we can compare values with variables and variables with other variables
const one = 1; const two = 2; console.log(one === two); console.log(one !== two); // false true
const petName = "Jessie"; const breed = "Labrador"; const age = 3; const petDescription = petName + " - " + breed + ", " + age; console.log(petDescription); // Jessie - Labrador, 3
const age = 3; const isPuppy = age <= 1; console.log(isPuppy); // false
✓ equality and comparison operators, boolean value <= and =>
console.log("\n"); // special display statement, line break?
✓ variable concatenation
.toFixed(2); // formats numbers to two decimal places // connect the value to this format using a period "."
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add learned declarations, etc.
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Mimo: semi-completed (15. JavaScript Basics)