neo neo - 5 months ago 12
HTML Question

Is javascript dependent on location of declaration ? weird behaviour on a javascript program

I was just going through a basic javasript program and what I did was simply moving the javascript declaration after body to before body and the javscript simply turned to produce error. According to my knowledge javascript is not altered by the location of declaration. If so why is this behaviour ?

<!DOCTYPE html>
<html>
<head>
<style>
/* 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(0,0,0,0.4); /* Black w/ opacity */
}

/* Modal Content */
.modal-content {
position: relative;
background-color: #fefefe;
margin: auto;
padding: 0;
border: 1px solid #888;
width: 80%;
box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2),0 6px 20px 0 rgba(0,0,0,0.19);
-webkit-animation-name: animatetop;
-webkit-animation-duration: 0.4s;
animation-name: animatetop;
animation-duration: 0.4s
}

/* Add Animation */
@-webkit-keyframes animatetop {
from {top:-300px; opacity:0}
to {top:0; opacity:1}
}

@keyframes animatetop {
from {top:-300px; opacity:0}
to {top:0; opacity:1}
}

/* The Close Button */
.close {
color: white;
float: right;
font-size: 28px;
font-weight: bold;
}

.close:hover,
.close:focus {
color: #000;
text-decoration: none;
cursor: pointer;
}

.modal-header {
padding: 2px 16px;
background-color: #5cb85c;
color: white;
}

.modal-body {padding: 2px 16px;}

.modal-footer {
padding: 2px 16px;
background-color: #5cb85c;
color: white;
}
</style>
</head>
<body>

<h2>Animated Modal with Header and Footer</h2>

<!-- Trigger/Open The Modal -->
<button id="myBtn">Open Modal</button>

<!-- The Modal -->
<div id="myModal" class="modal">

<!-- Modal content -->
<div class="modal-content">
<div class="modal-header">
<span class="close">×</span>
<h2>Modal Header</h2>
</div>
<div class="modal-body">
<p>Some text in the Modal Body</p>
<p>Some other text...</p>
</div>
<div class="modal-footer">
<h3>Modal Footer</h3>
</div>
</div>

</div>

<script>
// Get the modal
var modal = document.getElementById('myModal');

// Get the button that opens the modal
var btn = document.getElementById("myBtn");

// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];

// 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 anywhere outside of the modal, close it
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
</script>

</body>
</html>


The simple code change I made...



<!DOCTYPE html>
<html>
<head>
<style>
/* 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(0,0,0,0.4); /* Black w/ opacity */
}

/* Modal Content */
.modal-content {
position: relative;
background-color: #fefefe;
margin: auto;
padding: 0;
border: 1px solid #888;
width: 80%;
box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2),0 6px 20px 0 rgba(0,0,0,0.19);
-webkit-animation-name: animatetop;
-webkit-animation-duration: 0.4s;
animation-name: animatetop;
animation-duration: 0.4s
}

/* Add Animation */
@-webkit-keyframes animatetop {
from {top:-300px; opacity:0}
to {top:0; opacity:1}
}

@keyframes animatetop {
from {top:-300px; opacity:0}
to {top:0; opacity:1}
}

/* The Close Button */
.close {
color: white;
float: right;
font-size: 28px;
font-weight: bold;
}

.close:hover,
.close:focus {
color: #000;
text-decoration: none;
cursor: pointer;
}

.modal-header {
padding: 2px 16px;
background-color: #5cb85c;
color: white;
}

.modal-body {padding: 2px 16px;}

.modal-footer {
padding: 2px 16px;
background-color: #5cb85c;
color: white;
}
</style>
</head>
<script>
// Get the modal
var modal = document.getElementById('myModal');

// Get the button that opens the modal
var btn = document.getElementById("myBtn");
// Get the <span> element that closes the modal
var span = document.getElementsByClassName("close")[0];

// 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 anywhere outside of the modal, close it
window.onclick = function(event) {
if (event.target == modal) {
modal.style.display = "none";
}
}
</script>
<body>

<h2>Animated Modal with Header and Footer</h2>

<!-- Trigger/Open The Modal -->
<button id="myBtn">Open Modal</button>

<!-- The Modal -->
<div id="myModal" class="modal">

<!-- Modal content -->
<div class="modal-content">
<div class="modal-header">
<span class="close">×</span>
<h2>Modal Header</h2>
</div>
<div class="modal-body">
<p>Some text in the Modal Body</p>
<p>Some other text...</p>
</div>
<div class="modal-footer">
<h3>Modal Footer</h3>
</div>
</div>

</div>

</body>
</html>

Answer

It is dependent. All your selectors will fail because the HTML elements they're trying to select don't exist at the time of the code execution.

The same goes for the listeners, except for the window listener, of course, because the window object is present when the page starts loading.


See the difference:

<script>
  alert(document.getElementById('e'));
</script>
<div id="e"></div>

and:

<div id="e"></div>
<script>
  alert(document.getElementById('e'));
</script>