JavaScript - the global and local variable dilemma

Question

JavaScript - the global and local variable dilemma

REVISED2: I'm encountering an issue with converting images to canvas using Pixastic in HTML5. How can I 'return' this converted image back to a global variable? Any suggestions?

<img id="mainIllustration" alt="main illustration" src="Img/Model01.png">
Illust...o_03.js (line 24)
<canvas id="mainIllustration" class="" width="278" height="659" style="" title="" tabindex="-1">
Illust...o_03.js (line 32)
<img id="mainIllustration" alt="main illustration" src="Img/Model01.png">
Illust...o_03.js (line 24)
<canvas id="mainIllustration" class="" width="278" height="659" style="" title="" tabindex="-1">
Illust...o_03.js (line 32)
<img id="mainIllustration" alt="main illustration" src="Img/Model01.png">
Illust...o_03.js (line 24)
<canvas id="mainIllustration" class="" width="278" height="659" style="" title="" tabindex="-1">

REVISED 1: It seems that the issue lies with Pixastic manipulating the image and not returning it to the global image variable (eMainIllustration). Any advice on how to solve this problem?

UPDATED MESSAGE:

Hello everyone,

I am working with the Pixastic library and facing confusion regarding global and local variables.

Below are two sets of code, one where the variable is globally defined as desired and another where it is locally defined.

The first code snippet works fine with the locally defined variable eMainIllustration and the function functions properly.

    var eDisplayTableSlideState = false;
    function displayTableSlideIn()
    {
        var eMainIllustration = document.getElementById("mainIllustration"); // eMainIllustration is locally defined
        if (eDisplayTableSlideState === false)
        {
            $("#displayTable").animate ({top: "-=33px", left: "+=66px", width: "-=198px", height: "-=48px"}, 750, "swing",function()
            {
                Pixastic.process (eMainIllustration,"blurfast", {amount: 0.1});
                return (eDisplayTableSlideState = true);
            });
        } else
        {
            $("#displayTable").animate ({top: "+=33px", left: "-=66px", width: "+=198px", height: "+=48px"}, 500, "swing",function()
            {
                Pixastic.revert(eMainIllustration);
            });
            return (eDisplayTableSlideState = false);
        }
    }

However, when the variable eMainIllustration is set globally, the code within the 'else' part of the function does not work. Why is that?

// eMainIllustration is locally defined
var eMainIllustration = document.getElementById("mainIllustration");
    var eDisplayTableSlideState = false;
    function displayTableSlideIn()
    {
        if (eDisplayTableSlideState === false)
        {
            $("#displayTable").animate ({top: "-=33px", left: "+=66px", width: "-=198px", height: "-=48px"}, 750, "swing",function()
            {
                Pixastic.process (eMainIllustration,"blurfast", {amount: 0.1});
                return (eDisplayTableSlideState = true);
            });
        } else
        {
            $("#displayTable").animate ({top: "+=33px", left: "-=66px", width: "+=198px", height: "+=48px"}, 500, "swing",function()
            {
                Pixastic.revert(eMainIllustration);
            });
            return (eDisplayTableSlideState = false);
        }
    }

Could the issue be related to not returning the state of the changed eMainIllustration in the first half of the function? How can I resolve this?

Thank you,

javascript variables global-variables local

Answer 1

Answer №1

Have you ever wondered what happens when you alert or console.log the variable "out" inside a function? I've had my fair share of struggles when it comes to defining global variables within functions.

My point is, sometimes the DOM might not be fully loaded yet. You can try using the following code snippet:

if(window.addEventListener) {
    window.addEventListener('DOMContentLoaded', function() {
        //The DOM is now ready. You can set your global variables' values here.
    });
} else {
    //If you're dealing with Internet Explorer, use the attachEvent method instead.
}

Answer 2

Have you ever wondered what happens when you alert or console.log the variable "out" inside a function? I've had my fair share of struggles when it comes to defining global variables within functions.

My point is, sometimes the DOM might not be fully loaded yet. You can try using the following code snippet:

if(window.addEventListener) {
    window.addEventListener('DOMContentLoaded', function() {
        //The DOM is now ready. You can set your global variables' values here.
    });
} else {
    //If you're dealing with Internet Explorer, use the attachEvent method instead.
}

Answer 3

Answer №2

One possible reason for this issue is the positioning of your Javascript code on the page.

If your code is placed at the top of the page, there might be a delay in loading the mainIllustration dom element before the script is executed.

Moving the code just above the closing body tag ensures that the variable will be populated as the entire dom will be loaded when the Javascript runs.

Therefore, if the code works inside a function, it means the dom is fully loaded before calling the function; however, it may not work if placed outside a function.

var eMainIllustration = document.getElementById("mainIllustration");

Edit

<script type="text/javascript">
    $(document).ready(function() {
        load("path_to_javasript");
     });
</script>

Answer 4

One possible reason for this issue is the positioning of your Javascript code on the page.

If your code is placed at the top of the page, there might be a delay in loading the mainIllustration dom element before the script is executed.

Moving the code just above the closing body tag ensures that the variable will be populated as the entire dom will be loaded when the Javascript runs.

Therefore, if the code works inside a function, it means the dom is fully loaded before calling the function; however, it may not work if placed outside a function.

var eMainIllustration = document.getElementById("mainIllustration");

Edit

<script type="text/javascript">
    $(document).ready(function() {
        load("path_to_javasript");
     });
</script>

Answer 5

Answer №3

After some careful consideration, I managed to solve the issue at hand.

For those who may be unsure about how Pixastic operates, allow me to share my insights and provide a solution to the problem I encountered.

The Pixastic blurfast (& blur) plugin's 'revert function' essentially restores the element to its original state. Essentially, it undoes all changes made by previous effects, reverting the element back to its original appearance without adding any new effects.

It is important to note that when applying a Pixastic effect, the image transitions into an HTML5 canvas element. When using the revert function, this transition is reversed, restoring the original 'image' in place of the canvas element.

The confusion around global and local variables was resolved by implementing 'return' at the end of the function. Interestingly, this aspect turned out not to be the root cause of the issue; rather, the problem lied in my incorrect attempt to implement the revert functionality.

I sincerely hope this explanation proves useful to someone facing a similar challenge.

Answer 6

After some careful consideration, I managed to solve the issue at hand.

For those who may be unsure about how Pixastic operates, allow me to share my insights and provide a solution to the problem I encountered.

The Pixastic blurfast (& blur) plugin's 'revert function' essentially restores the element to its original state. Essentially, it undoes all changes made by previous effects, reverting the element back to its original appearance without adding any new effects.

It is important to note that when applying a Pixastic effect, the image transitions into an HTML5 canvas element. When using the revert function, this transition is reversed, restoring the original 'image' in place of the canvas element.

The confusion around global and local variables was resolved by implementing 'return' at the end of the function. Interestingly, this aspect turned out not to be the root cause of the issue; rather, the problem lied in my incorrect attempt to implement the revert functionality.

I sincerely hope this explanation proves useful to someone facing a similar challenge.

JavaScript - the global and local variable dilemma

Answer №1

Answer №2

Answer №3

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