summary.md

Summary - Part II: JavaScript for Programmers

Chapter 5: Functions

5.1 Defining Functions

first class objects

functions that can be stored in variables or as properties or passed as arguments to other functions

function definition aka function declaration

function assert(message, expr) {
  if (!expr) {
    throw new Error(message)
  }
  assert.count++

  return true
}

assert.count = 0

function definitions start with the function keyword

assert is the function identifier

functions can have one or more formal parameters called arguments

functions have a body between {}

functions may return something or undefined by default

functions can have properties like count

function expression

anonymous function assigned to a variable

var sum = function(a, b) {
  return a + b
}

anonymous function called immediately

(function () {
  console.log('Hello!')
})()

anonymous function as object property

var calculator = {
  sum: function (a, b) {
    return a + b
  },
  times(a, b) { // ES6 Syntax
    return a * b
  }
}
console.log(calculator.sum(5, calculator.times(3, 5))) // 20

anonymous function passed as argument to another function

function say(something) {
  if (typeof something == 'function') something()
}

say(function() {
  console.log('Hi!')
})

anonymous function returned from another function

function times(n) {
  return function (m) {
    return n * m
  }
}

console.log(times(3)(5)) // 15

5.2 Calling Functions

formal parameters

are those specified when declaring a function. a and b are the formal parameters in the function below

function sum(a, b) { return a + b }

arguments object

every function has an Array-like object called arguments containing the arguments passed to a function

function sum() { return arguments[0] + arguments[1] }
console.log(sum(2, 3)) // 5

5.3 Scope and Execution Context

types of scope

global

function

block (new in ECMAScript 6)

5.4 The this Keyword

this trick to implicitly set this is awesome

function addToArray() {
  var targetArr = arguments[0];
  arguments.slice = Array.prototype.slice;
  var add = arguments.slice(1);
  return targetArr.concat(add);
}