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How to close modal when <a> inside <li> is clicked?

I have managed to create a modal cum tab.
When user clicks the black color button, a modal appears with the list options. And as per user's selection content is shown.
I'm sharing the entire code below.
// Get the modal
var modal = document.getElementById("myModal");
// Get the button that opens the modal
var btn = document.getElementById("modalbtn");
// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];
// Get the li links that will change tabs
var link = document.getElementsByClassName("modallink");
// When the user clicks the button, open the modal
btn.onclick = function() {
modal.style.display = "block";
}
// When the user clicks on <span> (x), close the modal
span.onclick = function() {
modal.style.display = "none";
}
// When the user clicks on <span> (x), close the modal
link.onclick = function() {
modal.style.display = "none";
}
// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
setButtonInnerText(document.querySelector(".dropbtn"))
function openPage(id, a) {
const p = document.querySelector("[tab-name='" + id + "']");
const tabs = document.querySelectorAll(".tabs .dl-tabcontent");
for (var x = 0; x < tabs.length; x++)
tabs[x].classList.add("d-none");
if (p !== null) {
document.querySelector(".dropbtn").innerHTML = a.innerHTML;
p.classList.remove("d-none");
}
}
function toggleDrop(drop) {
drop.classList.toggle("d-none");
drop.onclick = function(e) {
drop.classList.add("d-none");
}
}
function setButtonInnerText(btn) {
const firstOption = btn.parentElement.querySelector("#drop a:first-child");
btn.innerHTML = firstOption.innerHTML;
}
h1,
h2,
h3 {
line-height: 1.35;
}
h1 {
font-size: 32px;
}
h2 {
font-size: 26px;
}
h3 {
font-size: 22px;
}
/* .modal-para{
font-size: 20px;
} */
#modalbtn {
margin: 0 auto;
display: block;
text-align: center;
background: #000;
color: #fff;
/* max-width: 200px; */
padding: 14px;
text-decoration: none;
cursor: pointer;
font-weight: 700;
border-radius: 3px;
outline: none;
border: 2px solid;
font-size: 17px
}
.modal {
display: none;
position: fixed;
z-index: 1;
padding-top: 0px;
left: 0;
top: 0;
width: 100%;
height: 100%;
overflow: auto;
background-color: rgba(0, 0, 0, 0.3);
-webkit-backdrop-filter: blur(5px);
backdrop-filter: blur(5px);
}
/* Modal Content */
.modal-content {
background-color: #fefefe;
margin: 50px auto 50px;
padding: 25px 35px;
/* border: 1px solid #888; */
border-radius: 12px 12px;
box-shadow: var(--shadow);
max-width: 500px;
/* width: 70%; */
}
/* The Close Button */
.close {
/* display: block; */
color: #aaaaaa;
font-size: 25px;
font-weight: bold;
float: right;
/* border: 3px solid; */
border-radius: 50px;
background: #e8e8ed;
padding: 3px 10px;
}
.close:hover,
.close:focus {
color: rgba(0, 0, 0, 0.72);
text-decoration: none;
cursor: pointer;
}
.modal-content-inner {
height: auto;
margin: 40px auto 10px;
max-width: 800px;
}
.modal-title {
margin-bottom: 10px;
}
.modal-ul {
padding: 0;
margin: 0 auto 0;
}
.modal-li {
list-style-type: none;
padding: 0;
}
.modal-li:not(:last-child) {
border-bottom: 1px solid var(--border-color);
}
.modal-li a {
text-decoration: none;
color: var(--ast-global-color-2);
padding: 17px 0;
display: block;
font-weight: 600;
font-size: 17px;
}
.modal-li a:hover {
color: var(--ast-global-color-1);
}
.d-none {
display: none;
}
.tabs {
max-width: 720px;
margin: 0 auto;
}
<!-- Trigger/Open The Modal -->
<button id="modalbtn" onclick="toggleDrop(document.querySelector('#drop'))" class="dropbtn">Open Modal</button>
<!-- The Modal -->
<div id="myModal" class="modal">
<!-- Modal content -->
<div class="modal-content">
<span class="close">×</span>
<div class="modal-content-inner">
<h3 class="modal-title">Select Option</h3>
<div id="drop" class="dropdown-content">
<ul class="modal-ul">
<li class="modal-li"><a id="modallink" href="#bird" onclick="openPage('dl-tabOne', this)">Click for Bird</li>
</a>
<li class="modal-li"><a id="modallink" href="#animal" onclick="openPage('dl-tabTwo', this)">Click for Animal
</li>
</a>
</ul>
</div>
</div>
</div>
</div>
<div class="tabs">
<!-- Bird Name -->
<div tab-name="dl-tabOne" class="dl-tabcontent">
Parrot
</div>
<!-- Animal Name -->
<div tab-name="dl-tabTwo" class="dl-tabcontent d-none">
Lion
</div>
</div>
Things are working fine but I want the modal to close automatically when the user clicks an option.
I'm new to JS. Kindly help me with the code that will close the modal when user clicks an option.
Thanks.

Just add this statement modal.style.display = "none"; as part of your openPage function as shown below :
function openPage(id, a) {
const p = document.querySelector("[tab-name='" + id + "']");
const tabs = document.querySelectorAll(".tabs .dl-tabcontent");
for (var x = 0; x < tabs.length; x++)
tabs[x].classList.add("d-none");
if (p !== null) {
document.querySelector(".dropbtn").innerHTML = a.innerHTML;
p.classList.remove("d-none");
}
modal.style.display = "none";
}

Just add this line
modal.style.display = "none";
on openPage() function
function openPage(id, a) {
const p = document.querySelector("[tab-name='" + id + "']");
const tabs = document.querySelectorAll(".tabs .dl-tabcontent");
for (var x = 0; x < tabs.length; x++)
tabs[x].classList.add("d-none");
if (p !== null) {
document.querySelector(".dropbtn").innerHTML = a.innerHTML;
p.classList.remove("d-none");
}
modal.style.display = "none";
}

HTML - Close pop up when clicking outside the div?

Got this script, but wondering what kind of function I need to add to make it close when clicking outside the box? Do I need to add another div and try to trigger that to make it close or?
Sorry I'm clueless considering writing javascript, I just understand how the events are created by the .onclick events but that's about it.
var closePopup = document.getElementById("popupclose");
var overlay = document.getElementById("overlay");
var popup = document.getElementById("popup");
var button = document.getElementById("button");
// Close Popup Event
closePopup.onclick = function () {
overlay.style.display = 'none';
popup.style.display = 'none';
};
// Show Overlay and Popup
button.onclick = function () {
overlay.style.display = 'block';
popup.style.display = 'block';
}
#overlay {
display: none;
position: absolute;
top: 0;
bottom: 0;
background: #99999945;
width: 100%;
height: 100%;
opacity: 0.8;
z-index: 100;
}
#popup {
display: none;
position: absolute;
top: 25%;
background: #fff;
width: 80%;
margin-left: 10%;
z-index: 200;
border-radius: 4px;
}
#popupclose {
float: right;
padding: 2px;
cursor: pointer;
}
.popupcontent {
padding: 10px;
}
#button {
cursor: pointer;
}
<button id="button" class="button btn--primary">Open div</button>
<div id="overlay"></div>
<div id="popup">
<div class="popupcontrols">
<span id="popupclose">Close X</span>
</div>
<div class="popupcontent">
Content inside popup
</div>
</div>

You could add a click-handler for the overlay element since that should cover all of the "outside" areas.
overlay.onclick = function () {
overlay.style.display = 'none';
popup.style.display = 'none';
};

API images not displayed within modal

I am a beginner and I am using several tutorials to learn and create a project. I am using the NASA APOD API to display images. However, I want to display the image when clicked within a modal. For some reason the image when clicked is displaying the modal, but without the image. How do I click on the image and display it within the modal.
const resultsNav = document.getElementById("resultsNav");
const favoritesNav = document.getElementById("favoritesNav");
const imagesContainer = document.querySelector(".images-container");
const saveConfirmed = document.querySelector(".save-confirmed");
const loader = document.querySelector(".loader");
// NASA API
const count = 3;
const apiKey = 'DEMO_KEY';
const apiUrl = `https://api.nasa.gov/planetary/apod?api_key=${apiKey}&count=${count}`;
let resultsArray = [];
let favorites = {};
// Show Content
function showContent(page) {
window.scrollTo({ top: 0, behavior: "instant" });
if (page === "results") {
resultsNav.classList.remove("hidden");
favoritesNav.classList.add("hidden");
} else {
resultsNav.classList.add("hidden");
favoritesNav.classList.remove("hidden");
}
loader.classList.add("hidden");
}
// Create DOM Nodes
function createDOMNodes(page) {
const currentArray =
page === "results" ? resultsArray : Object.values(favorites);
currentArray.forEach((result) => {
// Card Container
const card = document.createElement("div");
card.classList.add("card");
// Link that wraps the image
const link = document.createElement("a");
// link.href = result.hdurl; -- full size image display when clicked
// Get the modal
var modal = document.getElementById("myModal");
// Get the image and insert it inside the modal - use its "alt" text as a caption
var img = document.getElementById("myImg");
var modalImg = document.getElementById("img01");
var captionText = document.getElementById("caption");
img.onclick = function(){
modal.style.display = "block";
modalImg.src = this.src;
captionText.innerHTML = this.alt;
}
// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];
// When the user clicks on <span> (x), close the modal
span.onclick = function() {
modal.style.display = "none";
}
// Image
const image = document.createElement("img");
image.src = result.url;
image.alt = "NASA Picture of the Day";
image.loading = "lazy";
image.classList.add("card-img-top");
// Card Body
const cardBody = document.createElement("div");
cardBody.classList.add("card-body");
// Card Title
const cardTitle = document.createElement("h5");
cardTitle.classList.add("card-title");
cardTitle.textContent = result.title;
// Save Text
const saveText = document.createElement("p");
saveText.classList.add("clickable");
if (page === "results") {
saveText.textContent = "Add To Favorites";
saveText.setAttribute("onclick", `saveFavorite('${result.url}')`);
} else {
saveText.textContent = "Remove Favorite";
saveText.setAttribute("onclick", `removeFavorite('${result.url}')`);
}
// Card Text
const cardText = document.createElement("p");
cardText.textContent = result.explanation;
// Footer Conatiner
const footer = document.createElement("small");
footer.classList.add("text-muted");
// Date
const date = document.createElement("strong");
date.textContent = result.date;
// Copyright
const copyrightResult =
result.copyright === undefined ? "" : result.copyright;
const copyright = document.createElement("span");
copyright.textContent = ` ${copyrightResult}`;
// Append everything together
footer.append(date, copyright);
cardBody.append(cardTitle, saveText, cardText, footer); //hide to make image display
link.appendChild(image);
card.append(link); // hide cardBody
// Append to image container
imagesContainer.appendChild(card);
});
}
// Update the DOM
function updateDOM(page) {
// Get favorites from local storage
if (localStorage.getItem("nasaFavorites")) {
favorites = JSON.parse(localStorage.getItem("nasaFavorites"));
}
imagesContainer.textContent = "";
createDOMNodes(page);
showContent(page);
}
// Get 10 images from NASA API
async function getNasaPictures() {
// Show Loader
loader.classList.remove("hidden");
try {
const response = await fetch(apiUrl);
resultsArray = await response.json();
updateDOM("results");
} catch (error) {
// Catch Error Here
}
}
// Add result to favorites
function saveFavorite(itemUrl) {
// Loop through the results array to select favorite
resultsArray.forEach((item) => {
if (item.url.includes(itemUrl) && !favorites[itemUrl]) {
favorites[itemUrl] = item;
// Show save confirmation for 2 seconds
saveConfirmed.hidden = false;
setTimeout(() => {
saveConfirmed.hidden = true;
}, 2000);
// Set Favorites in Local Storage
localStorage.setItem("nasaFavorites", JSON.stringify(favorites));
}
});
}
// Remove item from favorites
function removeFavorite(itemUrl) {
if (favorites[itemUrl]) {
delete favorites[itemUrl];
localStorage.setItem("nasaFavorites", JSON.stringify(favorites));
updateDOM("favorites");
}
}
// On Load
getNasaPictures();
.container {
display: grid;
grid-template-columns: 1fr;
grid-template-rows: 3% 1fr 0.1fr;
gap: 0px 0px;
grid-auto-flow: row;
grid-template-areas:
"header"
"content"
}
.hero {
grid-area: hero;
background-color: blue;
}
.content {
grid-area: content;
background-color: orange;
align-self: center;
justify-self: center;
}
html {
box-sizing: border-box;
}
body {
margin: 0;
background: whitesmoke;
overflow-x: hidden;
font-family: Verdana, sans-serif;
font-size: 1rem;
line-height: 1.8rem;
}
.loader {
position: fixed;
z-index: 40;
background: whitesmoke;
height: 100vh;
width: 100vw;
display: flex;
justify-content: center;
align-items: center;
}
/* Navigation */
.navigation-container {
position: fixed;
top: 0;
}
.navigation-items {
display: flex;
justify-content: center;
}
.background {
background: whitesmoke;
position: fixed;
right: 0;
width: 100%;
height: 60px;
z-index: -1;
}
.clickable {
color: #0b3d91;
cursor: pointer;
user-select: none;
}
.clickable:hover {
color: #fc3d21;
}
/* Images Container */
.images-container {
display: grid;
grid-template-columns: repeat(3, 1fr);
}
.card {
margin: 10px 10px 10px;
width: 300px;
height: 300px;
}
.card-img-top {
width: 300px;
height: 300px;
}
.card-body {
padding: 20px;
}
.card-title {
margin: 10px auto;
font-size: 24px;
}
/* Save Confirmation */
.save-confirmed {
background: white;
padding: 8px 16px;
border-radius: 5px;
box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2);
transition: 0.3s;
position: fixed;
bottom: 25px;
right: 50px;
z-index: 500;
}
/* Hidden */
.hidden {
display: none;
}
.brand {
float: right;
}
.fave {
margin-right: 50%;
}
#myImg {
border-radius: 5px;
cursor: pointer;
transition: 0.3s;
}
/* #myImg:hover {opacity: 0.7;} */
/* The Modal (background) */
.modal {
display: none;
/* Hidden by default */
position: fixed;
/* Stay in place */
z-index: 1;
/* Sit on top */
padding-top: 100px;
/* Location of the box */
left: 0;
top: 0;
width: 100%;
/* Full width */
height: 100%;
/* Full height */
overflow: auto;
/* Enable scroll if needed */
background-color: rgb(0, 0, 0);
/* Fallback color */
background-color: rgba(0, 0, 0, 0.9);
/* Black w/ opacity */
}
/* Modal Content (image) */
.modal-content {
margin: auto;
display: block;
width: 80%;
max-width: 700px;
}
/* Caption of Modal Image */
#caption {
margin: auto;
display: block;
width: 80%;
max-width: 700px;
text-align: center;
color: #ccc;
padding: 10px 0;
height: 150px;
}
/* The Close Button */
.close {
position: absolute;
top: 15px;
right: 35px;
color: #f1f1f1;
font-size: 40px;
font-weight: bold;
transition: 0.3s;
}
.close:hover,
.close:focus {
color: #bbb;
text-decoration: none;
cursor: pointer;
}
/* 100% Image Width on Smaller Screens */
#media only screen and (max-width: 700px) {
.modal-content {
width: 100%;
}
}
<!-- Loader -->
<div class="loader hidden">
<img src="rocket.svg" alt="Rocket Icon" />
</div>
<!-- Container -->
<div class="container">
<div class="header">
<div class="navigation-container">
<span class="background"></span>
<!-- Results Nav -->
<span class="navigation-items" id="resultsNav">
</span>
<!-- Favorites Nav -->
<span class="navigation-items hidden" id="favoritesNav">
</span>
</div>
</div>
<div class="content">
<div class="container-fluid">
<div class="row">
<div class="column">
<div id="myImg" alt="Snow" class="images-container"></div>
</div>
</div>
</div>
</div>
<!-- The Modal -->
<div id="myModal" class="modal">
<span class="close">×</span>
<img class="modal-content" id="img01">
<div id="caption"></div>
</div>
</div>

In your img.onclick function/event listener (at line 51 of your JS), your this points to the parent instead of the image itself.
For a quick fix, try replacing your this with event.target (Basically, event.target.src in place of this.src and event.target.alt in place of this.alt at lines 56 and 57 of your current JS Fiddle)

Opening an external website in a modal popup

I know that Click here opens the link in a new tab (default behaviour in Chrome and Firefox) and that
<a href="http://www.example.com" onclick="window.open('http://www.example.com',
'newwindow', 'width=700,height=500'); return false;">Click here</a>
opens it in a new window.
But how to open an external page in a modal popup (centered on screen, rest of the original page "darkened")?
Is there a nice way to do it?
I tried the following code, but it doesn't seem to be working (click: popup opens, reclick, it closes, reclick on link: it doesn't open anymore. Also the iframe doesn't load).
document.getElementById("a").onclick = function(e) {
e.preventDefault();
document.getElementById("popup").style.display = "block";
document.getElementById('iframe').src = "http://example.com";
document.getElementById('page').className = "darken";
setTimeout(function() {
document.getElementById('page').onclick = function() {
document.getElementById("popup").style.display = "none";
document.getElementById('page').className = "";
}
}, 100);
return false;
}
#popup {
display: none;
border: 1px black solid;
width: 400px; height: 200px;
top:20px; left:20px;
background-color: white;
z-index: 10;
padding: 2em;
position: fixed;
}
.darken { background: rgba(0, 0, 0, 0.7); }
#iframe { border: 0; }
html, body, #page { height: 100%; }
<div id="page">
Click me<br>
Hello<br>
Hello<br>
<div id="popup">
External website:
<iframe id="iframe"></iframe>
</div>
</div>

Based on Sphinx's great answer, here is what I'll use to create a modal popup displaying an external website in a iframe with a dark background for the rest of the page when the popup is open:
document.getElementById("link").onclick = function(e) {
e.preventDefault();
document.getElementById("popupdarkbg").style.display = "block";
document.getElementById("popup").style.display = "block";
document.getElementById('popupiframe').src = "http://example.com";
document.getElementById('popupdarkbg').onclick = function() {
document.getElementById("popup").style.display = "none";
document.getElementById("popupdarkbg").style.display = "none";
};
return false;
}
window.onkeydown = function(e) {
if (e.keyCode == 27) {
document.getElementById("popup").style.display = "none";
document.getElementById("popupdarkbg").style.display = "none";
e.preventDefault();
return;
}
}
#popup { display: none; position: fixed; top: 12%; left: 15%; width: 70%; height: 70%; background-color: white; z-index: 10; }
#popup iframe { width: 100%; height: 100%; border: 0; }
#popupdarkbg { position: fixed; z-index: 5; left: 0; top: 0; width: 100%; height: 100%; overflow: hidden; background-color: rgba(0,0,0,.75); display: none; }
<div id="main">
Click me<br>
</div>
<div id="popup"><iframe id="popupiframe"></iframe></div>
<div id="popupdarkbg"></div>

The root cause is page.onclick is registered after popup window is open at the first time, then the following 'open popup' will trigger a.onclick and page.onclick in a row, that caused the popup window is open then is closed directly.
The simple solution is add one parameter to control the state of the popup. if the popup is closed, do nothing in page.onclick.
To remove setTimeout, there are two solution:
added another parameter to control the state of the popup initialization.
Don't make <div id="page"> is the parent of <a id="popup">, so <a id="popup"> will not be triggered when clicked <div id="page">.
Below are two solutions:
I prefer the Solution2, it is better decoupling than
Solution1, every component foucs on its own jobs.
Solution 1: added isInit as the indicator if the popup already finished initialization.
PS: In the comment, you mentioned close the popup only when click on <div id="page">, to implement this in solution1, I think you have to bind the event =mouseout, mouseenter to judge where the mouse clicks.
document.getElementById("a").onclick = function(e) {
e.preventDefault();
var isInit = true; // indicates if the popup already been initialized.
var isClosed = false; // indicates the state of the popup
document.getElementById("popup").style.display = "block";
document.getElementById('iframe').src = "http://example.com";
document.getElementById('page').className = "darken";
document.getElementById('page').onclick = function() {
if(isInit){isInit=false;return;}
if(isClosed){return;} //if the popup is closed, do nothing.
document.getElementById("popup").style.display = "none";
document.getElementById('page').className = "";
isClosed=true;
}
return false;
}
#popup {
display: none;
border: 1px black solid;
width: 400px; height: 200px;
top:20px; left:20px;
background-color: white;
z-index: 10;
padding: 2em;
position: fixed;
}
.darken { background: rgba(0, 0, 0, 0.7); }
#iframe { border: 0; }
html, body, #page { height: 100%; }
<div id="page">
Click me<br>
Hello<br>
Hello<br>
<div id="popup">
External website:
<iframe id="iframe"></iframe>
</div>
</div>
Solution 2: make <div id="page"> and <a id="popup"> is cousin not parent relations.
document.getElementById("popup").showpopup = function() {
document.getElementById("popup").style.display = "block";
document.getElementById('iframe').src = "http://example.com";
document.getElementById('page').className = "darken";
document.getElementById("page").style.display = "block";
}
document.getElementById("a").onclick = function(e) {
e.preventDefault();
document.getElementById("popup").showpopup();
}
document.getElementById('page').onclick = function() {
if(document.getElementById("popup").style.display == "block") {
document.getElementById("popup").style.display = "none";
document.getElementById("page").style.display = "none";
document.getElementById('page').className = "";
}
};
#popup {
display: none;
border: 1px black solid;
width: 400px; height: 200px;
top:20px; left:20px;
background-color: white;
z-index: 10;
padding: 2em;
position: fixed;
}
#page {
display: none;
width: 100%; height: 100%;
top:0px; left:0px;
z-index: 9;
padding: 2em;
position: absolute;
}
.darken { background: rgba(0, 0, 0, 0.7); }
#iframe { border: 0; }
html, body, #page { height: 100%; }
Click me<br>
Hello<br>
Hello<br>
<div id="page">
</div>
<div id="popup">
External website:
<iframe id="iframe"></iframe>
</div>

document.getElementById("a").onclick = function(e) {
e.preventDefault();
var isInit = true; // indicates if the popup already been initialized.
var isClosed = false; // indicates the state of the popup
document.getElementById("popup").style.display = "block";
document.getElementById('iframe').src = "http://example.com";
document.getElementById('page').className = "darken";
document.getElementById('page').onclick = function() {
if(isInit){isInit=false;return;}
if(isClosed){return;} //if the popup is closed, do nothing.
document.getElementById("popup").style.display = "none";
document.getElementById('page').className = "";
isClosed=true;
}
return false;
}
#popup {
display: none;
border: 1px black solid;
width: 400px; height: 200px;
top:20px; left:20px;
background-color: white;
z-index: 10;
padding: 2em;
position: fixed;
}
.darken { background: rgba(0, 0, 0, 0.7); }
#iframe { border: 0; }
html, body, #page { height: 100%; }
<div id="page">
Click me<br>
Hello<br>
Hello<br>
<div id="popup">
External website:
<iframe id="iframe"> height=“200”</iframe>
</div>
</div>

How to load a iframe only on button click

I want a youtube video Iframe only when "Watch Video" Button is clicked. Currently the video iframe loads in the background, when the page loads.
Note: I do not mean, play the video on button click. I mean, load the iframe on button click
https://jsfiddle.net/kz0xxe22/
// Get the modal
var modal = document.getElementById('trailerdivbox');
// Get the button that opens the modal
var btn = document.getElementById("watchbutton");
// When the user clicks the button, open the modal
btn.onclick = function() {
modal.style.display = "block";
}
var trailerbox = document.getElementById("close");
trailerbox.onclick = function() {
modal.style.display = "none";
}
// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
/* Watch Trailer Button CSS */
#watchbutton {
background-color: #f2f2f2;
color: red;
font-weight: 600;
border: none;
/* This one removes the border of button */
padding: 10px 12px;
}
#watchbutton:hover {
background-color: #e2e2e2;
cursor: pointer;
}
#trailerdivbox {
display: none;
width: 100%;
height: 100%;
position: fixed;
overflow: auto;
/* Enable Scrolling */
background-color: rgb(0, 0, 0);
/* Fallback color */
background-color: rgba(0, 0, 0, 0.4);
/* Black w/ opacity */
}
.videoWrapper {
position: relative;
padding-bottom: 56.25%;
/* 16:9 */
padding-top: 25px;
height: 0;
}
.videoWrapper iframe {
position: absolute;
max-width: 560px;
max-height: 315px;
width: 95%;
height: 95%;
left: 0;
right: 0;
margin: auto;
}
<button id="watchbutton">Watch Trailer &#9658</button>
<div id="close">
<div id="trailerdivbox">
<div class="videoWrapper">
<iframe class="trailervideo" width="560" height="315" src="https://www.youtube.com/embed/TDwJDRbSYbw" frameborder="0" allowfullscreen></iframe>
</div>
</div>
</div>

You can change the src attribute to a data-src, then when you click the button, set src to data-src
// Get the modal
var modal = document.getElementById('trailerdivbox');
// Get the button that opens the modal
var btn = document.getElementById("watchbutton");
var trailer = document.getElementById('trailervideo');
// When the user clicks the button, open the modal
btn.onclick = function() {
modal.style.display = "block";
trailer.setAttribute('src', trailer.getAttribute('data-src'));
}
var trailerbox = document.getElementById("close");
trailerbox.onclick = function() {
modal.style.display = "none";
}
// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
/* Watch Trailer Button CSS */
#watchbutton {
background-color: #f2f2f2;
color: red;
font-weight: 600;
border: none;
/* This one removes the border of button */
padding: 10px 12px;
}
#watchbutton:hover {
background-color: #e2e2e2;
cursor: pointer;
}
#trailerdivbox {
display: none;
width: 100%;
height: 100%;
position: fixed;
overflow: auto;
/* Enable Scrolling */
background-color: rgb(0, 0, 0);
/* Fallback color */
background-color: rgba(0, 0, 0, 0.4);
/* Black w/ opacity */
}
.videoWrapper {
position: relative;
padding-bottom: 56.25%;
/* 16:9 */
padding-top: 25px;
height: 0;
}
.videoWrapper iframe {
position: absolute;
max-width: 560px;
max-height: 315px;
width: 95%;
height: 95%;
left: 0;
right: 0;
margin: auto;
}
<button id="watchbutton">Watch Trailer &#9658</button>
<div id="close">
<div id="trailerdivbox">
<div class="videoWrapper">
<iframe id="trailervideo" class="trailervideo" width="560" height="315" data-src="https://www.youtube.com/embed/TDwJDRbSYbw" frameborder="0" allowfullscreen></iframe>
</div>
</div>
</div>

Simplest thing to do is add the src attribute when clicking the "Watch Trailer" button! :)
// Get the modal
var modal = document.getElementById('trailerdivbox');
// Get the button that opens the modal
var btn = document.getElementById("watchbutton");
// When the user clicks the button, open the modal
btn.onclick = function() {
modal.style.display = "block";
//Add "src" attribute by getting the video and setting it with setAttribute.
document.getElementsByClassName('trailervideo')[0].setAttribute('src', 'https://www.youtube.com/embed/TDwJDRbSYbw');
}
var trailerbox = document.getElementById("close");
trailerbox.onclick = function() {
modal.style.display = "none";
}
// When the user clicks anywhere outside of the modal, close it
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
/* Watch Trailer Button CSS */
#watchbutton {
background-color:#f2f2f2;
color:red;
font-weight:600;
border: none; /* This one removes the border of button */
padding: 10px 12px;
}
#watchbutton:hover {
background-color:#e2e2e2;
cursor:pointer;
}
#trailerdivbox {
display:none;
width: 100%;
height:100%;
position:fixed;
overflow: auto; /* Enable Scrolling */
background-color: rgb(0,0,0); /* Fallback color */
background-color: rgba(0,0,0,0.4); /* Black w/ opacity */
}
.videoWrapper {
position: relative;
padding-bottom: 56.25%; /* 16:9 */
padding-top: 25px;
height: 0;
}
.videoWrapper iframe {
position: absolute;
max-width:560px;
max-height:315px;
width: 95%;
height: 95%;
left:0;
right:0;
margin:auto;
}
<button id="watchbutton">Watch Trailer &#9658</button>
<div id="close">
<div id="trailerdivbox" >
<div class="videoWrapper">
<iframe class="trailervideo" width="560" height="315" frameborder="0" allowfullscreen></iframe>
</div>
</div>
</div>