Things I Don't Understand/Questions

  1. I don't understand the purpose of a symbol in js

Answers

  1. I still don't really understand why we use symbols in JavaScript. I looked on some other websites and it seems like they're used when you want something to be unique.

JavaScript Notes

Reserved JavaScript Words

abstract, await, boolean, break, byte, case, catch, char, class, const, continue, debugger, default, delete, do, double, else, enum, export, extends, false, final, finally, float, for, function, goto, if, implements, import, in instanceof, int, interface, let, long, native, new, null, package, private, protected, public, return, short, static, super, switch, synchronized, this, throw, throws, transient, true, try, typeof, var, volatile, void, while, with, yield

Template Literals

` is used to deliminate a string: `hello`
This makes it so you can use both kinds of quotes: `She said, "It's Me!"`
They also make it so a JavaScript expression can be inserted inside a string and the result will be displayed:
const name = `Siri`;
`Hello ${ name }!`;
'Hello Siri!'

Converting Strings to Numbers and Numbers to Strings

To convert a string to a number, use the Number method: Number('23');
To convert a number to a string, use the String function: String(3);

Parsing

The parseInt() function converts a string representation of a numerical value back into a number: parseInt('23',10);
The parseFloat() function does almost the same thing but converts the string to a floating point number.

Exponents

Don't use ^ for exponents. Use **

Soft vs Hard

It is better to use hard equality (===) rather than soft (==). Hard equality checks for the same datatype.

Arrays

Create an Array

const myArray = [];

Initialize an Array

const heroes = [];

Adding to an Array

heroes[0] = 'Superman';

Create Array Literals

const avengers = ['Captain America', 'Iron Man', 'Thor', 'Hulk'];

Removing Array Values

delete avengers[3];

Find array length

avengers.length;

Find Last Item in Array

avengers[avengers.length - 1];

Change array size

avengers.length = 8;

Remove Last Item From Array

avengers.length = 8;

Remove First Item in Array

avengers.shift();

Append New Value to End of Array

avengers.push('Thor');

Append New Value to Beginning of Array

avengers.unshift('Captain America');

Turn the Values in the Array Into a Single String (values seperated by commas)

avengers.join();

Turn the Values in the Array Into a Single String (values seperated by whatever you specify)

avengers.join(' & ');

Check to see if a value is in an array. It will return the postion of the item. If the item isn't there, it will return -1

avengers.indexOf('Iron Man');

Create an Array of Arrays/Multidimensional Array

const coordinates = [[1,3],[4,2]];
Access the multidimensional array by refering to the items place in the outer array then the place in the inner: coordinates[0][0]; (The first value of the first array)

Sets

A set is a collection of unique values (no multiple values).

Create a Set

const list = new Set();

Adding Values to Set

list.add(1); Or Multiple values: list.add(2).add(3).add(4);
If you add a string in a set, it will be added as separate letters. To add words: const words = new Set().add('the').add('quick').add('brown').add('fox')

Remove Value From Set

jla.delete('Superman');

Convert Set to Array

const shoppingSet = new Set().add('Apples').add('Bananas').add('Beans');

Switch Statement

switch (number) {
case 4:
console.log('You rolled a four');
break;
case 5:
console.log('You rolled a five');
break;
case 6:
console.log('You rolled a six');
break;
default:
console.log('You rolled a number less than four');
break;
}

Loops

While Loops

let bottles = 10;
while (bottles > 0){
console.log(`There were ${bottles} green bottles, hanging on a wall. And if one green bottle should
accidentally fall, there'd be ${bottles-1} green bottles hanging on the wall`);
bottles--;
}
Or
let bottles = 11;
while (--bottles){
console.log(`There were ${bottles} green bottles, hanging on a wall. And if one green bottle should accidentally fall, there'd be ${bottles-1} green bottles hanging on the wall`);
}

Do...While Loop

let bottles = 10;
do {
console.log(`There were ${bottles} green bottles, hanging on a wall. And if one green bottle should
accidentally fall, there'd be ${bottles-1} green bottles hanging on the wall`);
bottles--;
} while (bottles > 0)

For Loop

for (let bottles = 10 ; bottles > 0 ; bottles--) {
console.log(`There were ${bottles} green bottles, hanging on a wall. And if one green bottle should accidentally fall, there'd be ${bottles-1} green bottles hanging on the wall`);
}

Loop Over Arrays

for(let i=0, max=avengers.length; i < max; i++){
console.log(avengers[i]);
}

Loop Over Sets

for(const letter of letters) {
console.log(letter);
}

Functions

Function Declaration

function hello(){
console.log('Hello World!');
}

Function Expressions

const goodbye = function(){
console.log('Goodbye World!');
};

Invoke a Function

hello();

Default Parameters

Provide a default parameter if no arguments are provided.
function hello(name='World') {
console.log(`Hello ${name}!);
}
If you call the function without parameters, you will get: 'Hello World'.

Arrow Functions

No parameters: const hello = () => alert('Hello World!');
One parameter: const square = x => x*x;
Two Parameters: const add = (x,y) => x + y;

Callbacks

A function passed as an argument to another function is a callback.
function sing(song) {
console.log(`I'm singing along to ${song}`);
}
sing('Let It Go')
Output: 'I'm singing along to Let It Go'
function sing(song,callback) {
console.log(`I'm singing along to ${song}.`);
callback();
}