javascript.md

Javascript

Variables

// let means you can change the value of the variable later on
let id = 123;
// ✅ this is allowed
id = 432;


// const means you are not allowed to change the value of the variable later on
const id = 123;
// ❌ this is not allowed
id = 432;

// var is an old way of defining variables, you should try to avoid it
var a = 123;

variables

• cannot start with numbers
• cannot contain symbols
• must be at least 1 character

// ✅ this is allowed
let x = 1;
let _ = 1;
let x1 = 1;
// ❌ this is not allowed
let % = 1;

Functions

Functions have 3 things.

• name.
• parameter list
• return value

// regular anonymous function
// it has no name
function () {}

// function declarations are hoisted to the top of the file
function customName () {

}

// arrow functions have no name and look like this
const var = () => {};

If a function has the async keyword in front of it, it will return a promise. It will also have the ability to use the keyword await to resolve other async functions

Examples

async function getCalculations(){
  await wait(5000);
}

Objects

Objects are intialized like this

const obj = {};

Objects can have key-values. Keys are mostly always strings. Values are any valid js value.

Accessing a value in an object

// Dot notation
// you can only use dot notation for keys that would be valid variable names
// you can define a key with non-valid variable names but you cannot use
// dot notation when accessing that key
const obj = {
  a: 1234,
  "%": 'abcd'
};
// ✅ this is allowed
console.log(obj.a)
// ❌ this is not allowed
console.log(obj.%)


// Bracket notation
const obj = {
  a: 5123,
  "!": "ABCD"
};
// ✅ this is allowed
console.log(obj['a'])
// ✅ this is also allowed
console.log(obj['!'])

Assigning a key-value in an object

// Dot notation
const obj = {};
obj.a = 1234;
/*
the object now looks like
{
  a: 1234
}
*/

// Bracket notation
const obj = {};
obj['a'] = 5123;
/*
the object now looks like
{
  a: 5123
}
*/

Strings

Strings can be defined in three ways.

// double quotes
"this is an example"
// single quotes
'this is an example'
// string interpolation example
let x = 12341234;
`this is an example of string interpolation ${x}`
// the resulting interpolated string looks like
"this is an example of string interpolation 12341234"

Values

The valid type of js values are

• numbers, 1
• strings, "", '', ``
• functions, function () {}, () => {}
• objects, {}
• arrays, []
• undefined
• null
• Infinity
• -Infinity
• NaN