FUNCTIONS

Objectives!

  • describe the concept of a function in one sentence
  • explain the syntax of a function
  • create a function
  • invoke a function
  • use the keyword return
  • add behavior with parameters and arguments
  • use the keyword arguments

What is a function?

A reusable sequence of instructions that achieve a specific task

Function Syntax

var myfunction = function () {
    BODY
}

Expression declaration

function as a part of a larger expression syntax (typically a variable assignment )

Function Syntax

function name () {
    BODY
}

statement declaration

Function Syntax

var func = x => x * x;                  
var func = (x, y) => { return x + y; };

Arrow, "fat arrow" syntax

Function Syntax

var func = new Function();

Not recommended.

Let's make some functions!

Write a function named "greet" that will print out "Hello World!"

function greet() {
    console.log("Hello World!");
}

Let's make some functions!

What will the console.log return?

var whisper = "Kittens are magic";

function yell() {
    whisper = whisper.toUpperCase();
    console.log(whisper);
}

console.log(whisper);

Why?

Invoking your function

What's different here?

var whisper = "Kittens are magic";

function yell() {
    whisper = whisper.toUpperCase();
    console.log(whisper);
}

yell()

Invoking your function

Write and invoke a function to print "Wizard cat"

var myPets = {
    Ginger: "dachshund/corgi",
    Ferdinand: "French bulldog",
    Zoey: "Australian cattle dog",
    Ben: "Wizard cat"
}

Invoking your function

Write and invoke a function to print "Wizard cat"

var myPets = [
    ["Ferdinand", "French bulldog", "cream"],
    ["Ginger", "dachshund/corgi", "red"],
    ["Zoey", "Australian cattle dog", "blue"],
    ["Ben", "Wizard cat", "white"]
];

Stretch: write a function that uses a loop to print each pet's name

Arguments and Parameters

Why use them? 

Makes your code dynamic and reusable

Arguments and Parameters

function myFunc (param1, param2) {
    console.log(param1);
    console.log(param2);
};


myFunc("argument1", "argument2")

Arguments and Parameters

function greet2 (name) {
    console.log("Hello, " + name);
};


greet2("Danny")

Define a function named "greet2" that will take a name as a parameter and print "Hello, <name>"

Then invoke it with a name as an argument.

return keyword

function greet2 (name) {
    return "Hi!";
    console.log("Hello, " + name);
};


greet2("Danny")

return keyword

returning something is the purpose of a function. 

FUNCTIONS

By Valerie Kraucunas

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FUNCTIONS

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