Mastering JS Functions Examples

callbacks_and_array_methods.js

// map examples
[1, 2, 3, 4].map(function(num) {
  return 2 * num;
});

[1, 2, 3, 4].map(function(num) {
  if (num % 2 === 0) return "even";
  else return "odd";
});

// example with named functions
function double(num) { return 2 * num; }
function triple(num) { return num * 3; }
function isEven(num) { return num % 2 === 0; }

[1,2,3,4].map(double);
[1, 2, 3, 4, 5, 6, 7].map(triple);
[1, 2, 3, 4, 5, 6, 7].map(isEven);

// filter examples
[1, 2, 3, 4].filter(function(num) {
  return num < 3;
});

[1, 2, 3, 4, 5, 6, 7].filter(isEven);

callbacks_and_timers.js

// anonymous callback
setTimeout(function() {
  console.log("hi!!!");
}, 1000);

// named callback
function friendlyGreeting() {
  console.log("OMG HI SO NICE TO SEE YOU!!!!!!!!!!!!!!");
}

setTimeout(friendlyGreeting, 2000);

callbacks_custom_hof.js

function add(x, y) {
  return x + y;
}

function subtract(x, y) {
  return x - y;
}

function doSomeMath(operation, x, y) {
  return operation(x, y);
}

// doSomeMath is a higher order function
// it can take add or subtract as a callback.
doSomeMath(add, 1, 4);
doSomeMath(subtract, 4, 2);

closure_bank.js

function makeBankAccount(pin) {
  var balance = 1000;

  var publicMethods = {
  	deposit: function(pinGuess, amount) {
      if (pinGuess !== pin) return "Invalid credentials";

      balance += amount;
      return "Deposit successful! Your balance is: " + balance;
    },
    withdraw: function(pinGuess, amount) {
      if (pinGuess !== pin) return "Invalid credentials";
      if (amount > balance) return "You don't have enough $$$";

      balance -= amount;
      return "Withdrawal successful! Your balance is: " + balance;
    }
  }

  return publicMethods;

}

// Matt gets a bank account!
var mattAccount = makeBankAccount("1234");

// Jimmy gets a bank account!
var jimmyAccount = makeBankAccount("1111");

closure_guessing_game.js

function guessingGame() {
  var randomNumber = Math.floor(Math.random() * 1000);

  return function guess(num) {
    if (num < randomNumber) {
      return "hahaha too low!";
    } else if (num > randomNumber) {
      return "lolz too high!"
    } else {
      return "Oh no, you have found my secret number, and it is " + randomNumber + ". :("
    }
  }
}

// newGame will have a randomNumber inside of it,
// but there's no way to deduce its value without
// playing (and winning) the game.
var newGame = guessingGame()

first_closure_example.js

function sayMyNameLater() {
  var firstName = "Matt";

  return function sayMyNameSayMyName() {
    console.log(firstName);
  }
}

var lolwut = sayMyNameLater();

function sayMyNameSayMyName() {
  console.log(firstName);
}

sayMyNameSayMyName(); // ReferenceError: firstName is not defined

lolwut(); // "Matt"

scope_examples.js

function matt() {
  var firstName = "Matt";
  console.log(firstName);
}

matt(); // logs "Matt"
console.log(firstName); // ReferenceError: firstName is not defined

var x = 1;

function foo() {
  var y = 2;

  function bar() {
    var x = 5;
    var z = 3; 
    console.log(x + y + z)
  }

  bar();

}

foo(); // 10

function sayMyName() {
  var firstName = "Matt";

  function sayMyNameSayMyName() {
    console.log(firstName);
  }
  
  sayMyNameSayMyName();
}

sayMyName(); // "Matt"