Client side programming

Exercise #3

slides.com/jkohlin/jsx3/live

clone an array

// You cannot copy arrays like you do with strings and numbers
x = 10;
y = x;
x = 32;
console.log( x+y ) // 42 not 64

foo = [3,2,1];
bar = foo;
bar.sort();
console.log(foo); // [1,2,3]
console.log(bar); // [1,2,3]


// This is a way to create a copy of an array

foo = [3,2,1];
bar = foo.slice(0);
bar.sort();
console.log(foo); // [3,2,1]
console.log(bar); // [1,2,3]

strings are a bit like arrays

// some array methods apply to strings as well
"hello world".length // 11
"hello world".indexOf("w") // 6


// strings can be converted to arrays .split(separator)
"hello-world".split("-") // ["hello", "world"]
"code".split("") // ["c", "o", "d", "e"]


// Access a letter from a string
var foo = "hello world";
var bar = foo[6]; // "w"

from string to array to string

var myString = "The weather is lovely in Sweden";
var myArray = myString.split(" ");
// ["The", "weather", "is", "lovely", "in", "Sweden"];

myArray[3] = "aweful";
// ["The", "weather", "is", "aweful", "in", "Sweden"];

myString = myArray.join(" ");
// "The weather is aweful in Sweden"

console.log(myArray.join("-"));
// "The-weather-is-aweful-in-Sweden"

Finding elements

var myMenu = document.querySelector("#main-menu")

document.querySelector()

returns the first element that match the CSS-selector-string passed in.

var myLinks = document.querySelectorAll("a")

document.querySelectorAll()

returns ALL elements that match, in an array.

change the content of an element

<div id="demo">
<h1>Existing content</h1>
</div>

var myDiv = document.querySelector('#demo');

myDiv.innerHTML = '<p> This is <em>new</em> content </p>';

Existing content

This is new content

<div id="demo">
<p> This is <em>new</em> content </p>
</div>

before

after

Browser output

What can we actually use arrays for?

Like in web design?

Give each button a different color

display their "name" when clicked

Function parameters

Let's talk about this exemple

var name = prompt("your name");
var age = prompt("your name");

function displayName(name, age) {
  if (age >=18) {
    return name + " you can drive";
  } else {
    return name + " you are only " + age
  }
}


alert( displayName(name, age) )

the different scopes

var name = prompt("your name"); // e.g. "Jane"
var age = prompt("your name");  // e.g.g "23"

function displayName(name, age) {
  if (age >=18) {
    return name + " you can drive";
  } else {
    return name + " you are only " + age
  }
}

alert(displayName(name, age))

arguments = function parameters

if you find parameter names confusing,

use the automatic array arguments

function display(a,b) {
  return arguments[0] + ": " + arguments[1];
}

display("Jane Doe", 23); // "Jane Doe: 23"

Old McDonalds farm

Log the song in the console.

The log should have all animals: cows, pigs, cats, dogs

Your code may only contain the chorus ONCE

Your code may only contain console.log() ONCE