Functions

function foo(a, b){}
foo.length // 2

function foo() {}
foo.name // "foo"

function foo({x, y = 5} = {}) {
  console.log(x, y);
}
foo() // undefined 5

function log(x, y = 'World') {
  console.log(x, y);
}
log('Hello') // Hello World
log('Hello', 'China') // Hello China
log('Hello', '') // Hello

#Arrow functions

setTimeout(() => {
  ···
})

#with parameters

readFile('text.txt', (err, data) => {
  ...
})

#implicit return

arr.map(n => n*2)
//no curly braces = implicit return
//Same as: arr.map(function (n) { return n\*2 })
arr.map(n => ({
  result: n*2
}))
//Implicitly returning an object requires parentheses around the object

Like a function, but preserves this. See: Arrow functions