A raptor is on the loose. Rawr! He wants to stomp the townspeople. Write JavaScript code to allow the raptor to eat them. The HTML and CSS are already written; start from this skeleton of attack.html. (sample solution)
Make it so that when the page first appears, 5 boys are visible in the town. There are already 5 persons in the HTML, but they have no gender. These are stored in the div
with id
of people
as div
s with the class
of person
. Assign them the additional class boy
when the page loads (while retaining the class person
).
<div id="people"> <!-- give these 5 divs the class 'boy' --> <div class="person"></div> <div class="person"></div> <div class="person"></div> <div class="person"></div> <div class="person"></div> </div>
classList
property.
window.onload = function() { prepopulate(); }; function prepopulate() { var people = document.querySelectorAll("#people .person"); for (var i = 0; i < people.length; i++) { people[i].classList.add("boy"); } }
Add! Adds 5 more boys to the page (Later we will make it so that you can add girls too!). A person is a div
with the classes of person
and a class of either boy
or girl
.
<button id="add">Add!</button>
window.onload = function() { prepopulate(); document.getElementById("add").onclick = populate; }; // Add! button event handler; adds 5 people of current gender function populate() { for (var i = 0; i < 5; i++) { var newPerson = document.createElement("div"); newPerson.classList.add("person"); newPerson.classList.add("boy"); document.getElementById("people").appendChild(newPerson); } }
Kill! Randomly "kills" 1/5 of the boys on the page. Kill them by giving them a class of splat
(in addition to their existing person
class, but in place of their gender class such as boy
or girl
).
<button id="kill">Kill!</button>
window.onload = function() { prepopulate(); document.getElementById("kill").onclick = kill; }; // Get all guys or girls and splat one fifth of them function kill() { var peeps = document.querySelectorAll("#people .boy"); for (var i = 0; i < peeps.length / 5; i++) { var randomIndex = Math.floor(Math.random() * peeps.length); peeps[randomIndex].classList.remove("boy"); peeps[randomIndex].classList.add("splat"); } }
Boys / Girls: Add a function that returns which gender is currently selected. Modify the code from your previous two exercises so that you can choose which gender to add or kill.
<label><input id="boys" type="radio" name="gender" /> Boys</label> <label><input id="girls" type="radio" name="gender" checked="checked" /> Girls</label>
// Helper function to get which gender is currently selected. // Use the return from this to parameterize populate() and kill(). function getGender() { if (document.getElementById("boys").checked) { return "boy"; } else { return "girl"; } }
Clean Up! Removes any dead splatted people from the page (any
div
s with class splat
).
<button id="cleanup">Clean up!</button>
removeChild
method.
window.onload = function() { prepopulate(); document.getElementById("cleanup").onclick = clearDead; }; // Clean up the dead! button event handler function clearDead() { var dead = document.querySelectorAll("#people .splat"); for (var i = 0; i < dead.length; i++) { dead[i].parentNode.removeChild(dead[i]); } }
Stomp! Makes the raptor move up or down by 75px and also kills 1/5 of both genders. The raptor is an img
tag with an id
of raptor
.
<button id="stomp">Stomp!</button>
top
style attribute to be either 10px
or 85px
.
window.getComputedStyle(element).propertyName
.
window.onload = function() { prepopulate(); document.getElementById("stomp").onclick = stomp; }; // Stomp! button event handler function stomp() { var raptor = document.getElementById("raptor"); var pxtop = parseInt(window.getComputedStyle(raptor).top); raptor.style.top = ((pxtop + 75) % 150) + "px"; splat("boy"); splat("girl"); }
Enrage! Applies the CSS class of enrage
to the raptor and the page's top h1
heading. In addition, the raptor should be made to be 50px wider than his current width. Clicking the button again removes the class from both elements and returns the width to its previous value. The h1
has an existing CSS class that should not be removed. You are guaranteed that there is exactly one h1
element on the page.
<button id="enrage">Enrage!</button>
function enrageRaptor() { var raptor = document.getElementById("raptor"); var width = parseInt(window.getComputedStyle(raptor).width); var h1 = document.querySelector("h1"); // If enraged -- go back to normal, else get ENRAGED if (raptor.classList.contains("enrage")) { raptor.classList.remove("enrage"); h1.classList.remove("enrage"); raptor.style.width = width - 50 + "px"; } else { raptor.classList.add("enrage"); h1.classList.add("enrage"); raptor.style.width = width + 50 + "px"; } }
Patrol! (advanced) Makes the raptor animate. He should move right by 4px every 20ms until his left
position style is at least 300px
, he should change directions and start patrolling to the left until his left
position is 10px
or less, at which point he stops patrolling.
<button id="patrol">Patrol!</button>
setInterval
method.
// Patrol! event handler code (advanced) var timer; function patrol() { clearInterval(timer); timer = setInterval(patrolRight, 20); } function patrolRight() { var raptor = document.getElementById("raptor"); var pxleft = parseInt(window.getComputedStyle(raptor).left); pxleft += 4; raptor.style.left = pxleft + "px"; if (pxleft >= 300) { clearInterval(timer); timer = setInterval(patrolLeft, 20); } }
function patrolLeft() { var raptor = document.getElementById("raptor"); var pxleft = parseInt(window.getComputedStyle(raptor).left); pxleft -= 4; raptor.style.left = pxleft + "px"; if (pxleft <= 10) { clearInterval(timer); raptor.style.top = "5px"; // Reset the Raptor raptor.style.left = "10px"; } }