JavaScript

Variable declarations

var

• function scoped

• can be redeclared and updated

• hoisted and initialized with undefined as a value

let

• block scoped

• declaring in a for loop, inside an if or in a plain block is not going to let the variable "escape" the block

• only use let to reassign the variable

• while let and const are hoisted but not initialized

const

• immutable

• block-scoped

• default to const

Array

• ​https://sdras.github.io/array-explorer/​

• ​https://flaviocopes.com/javascript-array/​

Object

• ​https://sdras.github.io/object-explorer/​

• ​https://codepen.io/thonly/pen/JOdwKM​

Promises

When you go to a restaurant, the hostess gives you a buzzer for your table. When the table is ready, the buzzer buzzes. You respond by sitting at the table.

The buzzer is a promise. It buzzes when the promise resolves, or is ready. The buzz is your handler.

var buzzer = new Promise();
​
fetchTableAsync(hostess => {
    var table = hostess.prepareTable();
    hostess.informServer();
    buzzer.resolve(table);
});
​
buzzer.then(table => me.sitAtTable(table));

• ​https://github.com/wbinnssmith/awesome-promises​

Currying

Currying is a process to reduce functions of more than one argument to functions of one argument with the help of lambda calculus.

multiply = (n, m) => (n * m)
multiply(3, 4) === 12 // true
​
curryedMultiply = (n) => ( (m) => multiply(n, m) )
triple = curryedMultiply(3)
triple(4) === 12 // true

• ​https://blog.benestudio.co/currying-in-javascript-es6-540d2ad09400​