Intro to
Functional
JavaScript

Bianca Gandolfo

JavaScript Evangelist

Hack Reactor

slides: http://bit.ly/func-slides

exercises: http://bit.ly/func-exercises

Who is this for?

2-6mos experience learning JavaScript

Completed JS tutorial like Codecademy, CodeSchool, Khan Academy, or Bloc.io

Want to solidify fundamentals

Looking for more practice

Interested in getting into Hack Reactor

@BiancaGando

Part 1

Review and solidify core JS principles with project.

Part 2

Get started with functional methods.

After

Use foundation to grow as a JS engineer.

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Anatomy

Scope

Overview

Local
Global
Nested Scopes
Precedence
Block Scope

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Local Scope

var func = function(){
  var local = true;
};

console.log(local);

var x = 'global!';

var x = 'global!';

//inside a function
function encapsulate(){

z = 'global here, too!';

}

var x = 'global!';

//inside a function
function encapsulate(){
  z = 'global here, too!';

  window.y = 'also global!';
}

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Global Scope

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Parent vs Child Scope

var g = 'global'; 

function blender(fruit) { 
  var b = fruit; 
  var y = 'yogurt';
 
  function bs() { 
    alert( b + ' and ' + y + ' makes ' + b + ' swirl'); 
  } 
  bs(); 
} 

blender('blueberry');

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Privacy

var g = 'global'; 

function blender(fruit) { 
  var b = fruit; 
  var y = 'yogurt';
 
  function bs() { 
    alert( b + ' and ' + y + ' makes ' + b + ' swirl'); 
  } 
  bs(); 
} 

blender('blueberry');

creating scopes

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Precedence

var g = "global";

function go() { 
  var l = "local";
  var g = "in here!";
  alert(g + " inside go");
}

go();
alert(g + " outside go");

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Block Scope

var inBlock = false;

for(var i = 0; i < 5; i++){
  var inBlock = true;
};

if(inBlock){
  console.log('Is there block scope? ' + !inBlock);
}

Exercise Time

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Questions

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Closure

Closure Example

var closureAlert = function(){
  var x = "Help! I'm a variable stuck in a closure!";
  var alerter = function(){
    alert(x);
  };
  alerter();
};

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Closure Example

var closureAlert = function(){
  var x = "Help! I'm a variable stuck in a closure!";

  var alerter = function(){
    alert(x);
  };

  setTimeout(alerter, 1000);

  console.log('will still run right after');
};

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Closure Example

var closureAlert = function(){ 
  var x = 0; 
  var alerter = function(){ 
    alert(++x); 
  }; 
  return alerter; 
}; 

var funcStorer = closureAlert(); 
var funcStorer2 = closureAlert(); 
funcStorer();

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Closure Example

var add = function(num){
  var num1 = num;

  var addToNum1 = function(num2){
    return num1 + num2;
  };

  return addToNum1;
};

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Closure Example

function counter() {
  var n = 0;
  return {
    count: function() { return ++n; },
    reset: function() { n = 0; }
  };
};

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Closure Example

function counter() {
  var n = 0;

  return {
    count: function() { return n++; },
    reset: function() { n = 0; }
  };
};

var c = counter(), d = counter(); c.count();

d.count();
c.reset();
c.count();
d.count();

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Recipe

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Execution

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Gotcha!

var sayAlice = function(){

  var makeLog = function() {
    console.log(alice);
  };

  var alice = 'Why hello there, Alice!';

  return makeLog;
};

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var makeStopwatch = function(){
  console.log('initialized');
  var elapsed = 0;
  console.log(elapsed);

  var stopwatch = function(){
    console.log('stopwatch');
    return elapsed;
  };

  var increase = function(){ elapsed++; };
  setInterval(increase, 1000);

  return stopwatch;

};

var x = makeStopwatch();

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Module Pattern

var Module = function(){

  var privateProperty = 'foo';

  function privateMethod(args){
    // do something
  };

  return {
    publicProperty: "",
    publicMethod: function(args){
      // do something
    },
    privilegedMethod: function(args){ 
      privateMethod(args); 
    }
  };
};

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Module Pattern

var Car = function(){

  var gasolineLevel = 10;

  function useGas(amt){
    if(gasolineLevel - amt < 0){ 
      console.log("out of gas :[");
    } else { 
      gasolineLevel -= amt; 
    }
  };

  return {
    radioStation: "104.5",

    changeStation: function(station){
      this.radioStation = station;
    },
    go: function(speed){ useGas(speed); }
  };
};

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Exercises

Questions

Higher- Order Functions and Callbacks

1. takes a function as an input (argument)

element.addEventListener("click", function(){

  console.log("element clicked!");

});

2. returns a function as the output

var add = function(num){
  var num1 = num;

  return addToNum1 = function(num2){
    return num1 + num2;
  };

};

Higher-Order Functions

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var ifElse = function(condition, isTrue, isFalse){

  if(condition){
    isTrue;
  } else {
    isFalse;
  }
};

ifElse(true,

 function(){ console.log(true);},

 function(){ console.log(false);}

);

Callbacks

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var ifElse = function(condition, isTrue, isFalse){
  if(condition){
    isTrue();
  } else {
    isFalse();
  }
};

var logTrue = function(){ console.log(true); };
var logFalse = function(){ console.log(false); };

ifElse(true,logTrue,logFalse);

Callbacks

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var increment = function(n){ return n + 1; };

var square = function(n){ return n*n; };

var doMathSoIDontHaveTo = function(n, func){ return func(n); };

doMathSoIDontHaveTo(5, square);

doMathSoIDontHaveTo(4, increment);

Passing Arguments

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var ifElse = function(condition, isTrue, isFalse){
  if(condition){
    isTrue();
  } else {
    isFalse();
  }
};

Passing Arguments

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var ifElse = function(condition, isTrue, isFalse, arg){
  if(condition){
    isTrue(arg);
  } else {
    isFalse(arg);
  }
};

Passing Arguments

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var ifElse = function(condition, isTrue, isFalse){
  if(condition){
    isTrue.apply(this, [].slice.call(arguments,3));
  } else {
    isFalse.apply(this, [].slice.call(arguments,3));
  }
};

[xtra credit]Passing Arguments

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Exercises

Questions

Underscore.js

underscore.js

What is it? a utility library that provides functional methods for you to use in your JS.

Where is it? http://underscorejs.org/

Include it in your HTML:

Annotated Source:
http://underscorejs.org/docs/underscore.html

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_.each() defined

_.each([1,2,3], function(val,i,list){ 
  console.log(val);
});

http://underscorejs.org/#each

Iterates over a list of elements, yielding each in turn to an iterator function.
Each invocation of iterator is called with three arguments: (element, index, list). If list is a JavaScript object, iterator's arguments will be (value, key, list).

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_.each() usage

//_.each(list, iterator)

var pocketmon = ['Charisaur', 'Bulbazard', 'Twomew'];

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_.each() usage

//_.each(list, iterator)

var pocketmon = ['Charisaur', 'Bulbazard', 'Twomew'];

var logger = function(val){
  console.log(val);
};

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_.each() usage

//_.each(list, iterator)

var pocketmon = ['Charisaur', 'Bulbazard', 'Twomew'];

var logger = function(val){
  console.log(val);
};

_.each(pocketmon,logger);

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Looping with _.each

function AnimalMaker(name) {
  return {   
    speak: function () { 
      console.log("my name is ", name); 
    } 
  }; 
}; 

var animalNames = ['', '', '']; 
var farm = []; 

for(var i = 0; i < animalNames.length; i++){ 
  farm.push(AnimalMaker(animalNames[i])); 
}

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Looping with _.each

function AnimalMaker(name) {

  return { 
    speak: function () { 
      console.log("my name is ", name); 
    } 
  };
};

var animalNames = ['', '', ''];

var farm = [];

_.each(animalNames, function (name) {
  farm.push(AnimalMaker(name));
});

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_.map() defined

_.map([1,2,3], function(v,i,list){console.log(v)})

http://underscorejs.org/#map

Produces a new array of values by mapping each value in list through a transformation function (iterator).
Each invocation of iterator is called with three arguments: (element, index, list). If list is a JavaScript object, iterator's arguments will be (value, key, list).

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_.map() usage

//_.map(list, iterator)

var pocketmon = ['Charisaur', 'Bulbazard', 'Twomew'];

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_.map() usage

//_.map(list, iterator)

var pocketmon = ['Charisaur', 'Bulbazard', 'Twomew'];

var excitedArr = function(val){
  return val + '!!!';
};

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_.map() usage

//_.map(list, iterator)

var pocketmon = ['Charisaur', 'Bulbazard', 'Twomew'];

var excitedArr = function(val){
  return val + '!!!';
};

var excitedPocketmon = _.map(pocketmon,excitedArr);

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Looping with _.map

function AnimalMaker(name) {
  return { 
    speak: function () { 
      console.log("my name is ", name); 
    } 
  };
};

var animalNames = ['', '', ''];

var farm = []

_.each(animalNames, function (name) {
  farm.push(AnimalMaker(name));
});

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Looping with _.map

function AnimalMaker(name) {
  return { 
    speak: function () { 
      console.log("my name is ", name); 
    } 
  };
};

var animalNames = ['', '', ''];

var farm = _.map(animalNames, function (name) {
  return AnimalMaker(name);
});

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_.map vs _.each

function AnimalMaker(name) {
  return { 
    speak: function () { 
      console.log("my name is ", name); 
    } 
  };
};

var animalNames = ['', '', ''];

var farm = _.map(animalNames, function (name) {
  return AnimalMaker(name);
});

_.each(farm, function (animal) {
  animal.speak();
});

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Intro to Functional JavaScript

Who is this for?

Part 1

Part 2

After

Anatomy

Scope

Overview

Local Scope

Global Scope

Parent vs Child Scope

Privacy

creating scopes

Precedence

Block Scope

Exercise Time

Questions

Closure

Closure Example

Closure Example

Closure Example

Closure Example

Closure Example

Closure Example

Recipe

Execution

Gotcha!

Module Pattern

Module Pattern

Exercises

Questions

Higher- Order Functions and Callbacks

Higher-Order Functions

Callbacks

Callbacks

Passing Arguments

Passing Arguments

Passing Arguments

[xtra credit]Passing Arguments

Exercises

Questions

Underscore.js

underscore.js

_.each() defined

_.each() usage

_.each() usage

_.each() usage

Looping with _.each

Looping with _.each

_.map() defined

_.map() usage

_.map() usage

_.map() usage

Looping with _.map

Looping with _.map

_.map vs _.each

Exercises

Questions

Intro to
Functional
JavaScript