lecture 3

slides.com/jkohlin/js-3/live

This week: Chapter 3

Till next week: Read chapter 4

but first, again, what do you know so far?

you know
while-loops

 

There's another cool version of it

var answer;

do {
    kiss();
} while( confirm("Do you want another one?") )

the do-while-loop

The bad boy of loops.

Do first - ask later. 

BTW

you know break?

 

There's another cool utility for those

outerLoop: 
while( confirm("continue?") ) {
    var answer = prompt("your name:");
    var loops = 0;
    while(loops < 5){
        loops += 1;
        if (answer == "Joe") {
            break outerLoop;
        }
    }
}

Labels

Add them just above a loop or, actually, any code block.

Then by adding break yourLabelName; you will jump to the end of that code block

BTW

one:
{
    var rnd = Math.random();
    if (rnd > 0.5) {
        break one;
    }
    console.log("rnd is less than 0.5");
}
console.log(rnd)

Functions

reusable save-for-later-code-blocks

Encapsulated scripts that won't run until you tell it to run, or until the user tells it to run. 

 

Functions can be versatile and dynamic by using parameters. That way, one function can do different things.

 

One of the most important part of a modern programming language.

var score = 0;
var gameOn = true;

while (gameOn == true) {

    if ( prompt("blue pill or red pill?") == "blue pill" ) {
        break;
    } else {
        score += 1;
    }
    if ( prompt("good or evil?") == "evil" ) {
        break;
    } else {
        score += 1;
    }
    if ( prompt("What is the answer?") == "42" ) {
        break;
    } else {
        score += 1;
    }
    gameOn = confirm("play again?")
}

here's What functions could do to this code:

use case 1: avoid repetition

var score = 0;
var gameOn = true;

function quizQuestion (q, a) {
    if ( prompt( q ) == a ) {
        break;
    } else {
        score += 1;
    }
}

while (gameOn == true) {

    quizQuestion( "blue pill or red pill?", "blue pill" );
    quizQuestion( "good or evil?", "evil" );
    quizQuestion( "What is the answer?", "42" );

    gameOn = confirm( "play again?" )
}

much cleaner!

<body>
  <button onclick="pling()">Pling</button>
</body>

use case 2: run later

function pling() {
  audioElement = document.querySelector("audio");
  audioElement.play();
}

use case 3: use complex code made by others

uint64_t s[2];
uint64_t next(void) {
  uint64_t s1 = s[0];
  uint64_t s0 = s[1];
  uint64_t result = s0 + s1;
  s[0] = s0;
  s1 ^= s1 << 23; // a
  s[1] = s1 ^ s0 ^ (s1 >> 17) ^ (s0 >> 26); // b, c
  return result;
}
Math.random(); // A lot easier than the code below
function     (            ) {





}

The function keyword begins a function definition

function bark(            ) {





}

Next we give the function a name, like bark

function bark(name, weight) {





}

We call these the parameters
and, separate, them, by, commas

function bark(name, weight) {
  if (weight > 20) {
    alert(name + " says WOOF WOOF");
  } else {
    alert(name + " says woof"):
  }
}

We call this the body of the function

A values journey from 

 arguments / PARAMETERS and variables

see page 90

The first argument you pass to a function will be the value of the first parameter.

Arguments

See page 83-86

Passing variables as arguments

Let's just, once and for all 

get expressions

Sort out the expresions

...so, functions can also return things,  
–Be an expression that turns into a value

var c = 4;
function foo(num) {
  return num/2;
}
var a = foo( c * 3 ) ;
var c = 4;
function foo(num) {
  return num/2;
  alert('boo hoo, I will not popup');
}
var a = foo( c * 3 ) ;

return...

also quits the function.

return works like break in a loop. It will return a value and then stop reading the rest of the code in the function

What happens if you call a function from within another function?!

😲😱

see page 98-108


var gName = "Jane";

function printer() {  
  var name = "Tarzan";
  verb = " loves "  
  console.log(name + verb + gName);
}

console.log(gName);

see page 98-108


var gName = "Jane";

function printer() {  
  var name = "Tarzan";
  verb = " loves "  
  console.log(name + verb + gName);
}

console.log(gName);

LOCAL

GLOBAL

If you forget the var keyword inside functions,

the variable will be declared in the global scope

Other resources

Lecture 3

By Johan Kohlin

Lecture 3

Functions

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