Accessing variables outside of a JavaScript function can be done by declaring the

Question

Accessing variables outside of a JavaScript function can be done by declaring the

Is it possible to access the img element outside of the createThumbnail function? That's the challenge I'm facing at the moment.

Custom Function

function generateThumbnail(){
    canvas.deactivateAll().renderAll(); 
    html2canvas($('#chartdiv'), {
        onrendered: function(canvas) {
            var image = canvas.toDataURL("image/png"),
                element = document.getElementById("thumbnail_img");
                element.src = image;
        }
    });
}

javascript

Answer 1

Answer №1

The ideal solution is to return an object so that you can utilize the createThumbnail function multiple times (which cannot be achieved with a global variable).

This approach ensures that your code remains clean and that the function does not rely on the global scope or global variables.

function createThumbnail(){
    canvas.deactivateAll().renderAll(); 
    var img = {}, elem;
    html2canvas($('#chartdiv'), {
        onrendered: function(canvas) {
            img.dataUrl = canvas.toDataURL("image/png"),
            elem = document.getElementById("thumbnail_img");
            elem.src = img;
        }
    });
    return img;
}

var img = createThumbnail();
var dataUrl = img.dataUrl; // contains the dataUrl from the canvas when onrendered was called

Answer 2

The ideal solution is to return an object so that you can utilize the createThumbnail function multiple times (which cannot be achieved with a global variable).

This approach ensures that your code remains clean and that the function does not rely on the global scope or global variables.

function createThumbnail(){
    canvas.deactivateAll().renderAll(); 
    var img = {}, elem;
    html2canvas($('#chartdiv'), {
        onrendered: function(canvas) {
            img.dataUrl = canvas.toDataURL("image/png"),
            elem = document.getElementById("thumbnail_img");
            elem.src = img;
        }
    });
    return img;
}

var img = createThumbnail();
var dataUrl = img.dataUrl; // contains the dataUrl from the canvas when onrendered was called

Answer 3

Answer №2

You have defined a local variable within the onrendered callback. It would be more efficient to move the variable declaration outside of the function and then assign it a value inside the function.

var img; //Declare empty variable here.

function createThumbnail(){
  canvas.deactivateAll().renderAll();
  html2canvas($('#chartdiv'), {
    onrendered: function(canvas) {
      var elem;
      img = canvas.toDataURL("image/png");
      elem = document.getElementById("thumbnail_img");
      elem.src = img;
    }
  });
}

For more information on closures, you can refer to this article

Answer 4

You have defined a local variable within the onrendered callback. It would be more efficient to move the variable declaration outside of the function and then assign it a value inside the function.

var img; //Declare empty variable here.

function createThumbnail(){
  canvas.deactivateAll().renderAll();
  html2canvas($('#chartdiv'), {
    onrendered: function(canvas) {
      var elem;
      img = canvas.toDataURL("image/png");
      elem = document.getElementById("thumbnail_img");
      elem.src = img;
    }
  });
}

For more information on closures, you can refer to this article

Answer 5

Answer №3

It is not possible by default because the img is contained within an anonymous function. To make it accessible from outside, you will need to assign it to a variable that can be accessed externally.

var externalImg;

function generatePreview(){
    canvas.deactivateAll().renderAll(); 
    html2canvas($('#chartdiv'), {
        onrendered: function(canvas) {
            var img = canvas.toDataURL("image/png"),
                elem = document.getElementById("preview_img");
                elem.src = img;
            externalImg = img;
        }
    });
}

Answer 6

It is not possible by default because the img is contained within an anonymous function. To make it accessible from outside, you will need to assign it to a variable that can be accessed externally.

var externalImg;

function generatePreview(){
    canvas.deactivateAll().renderAll(); 
    html2canvas($('#chartdiv'), {
        onrendered: function(canvas) {
            var img = canvas.toDataURL("image/png"),
                elem = document.getElementById("preview_img");
                elem.src = img;
            externalImg = img;
        }
    });
}

Accessing variables outside of a JavaScript function can be done by declaring the

Custom Function

Answer №1

Answer №2

Answer №3

Similar questions

No response from jQuery's $.getJSON() function

The ngFor directive is not compatible with third-party library elements

How can one determine the dimensions of the browser window using a property?

Utilize React Redux to send state as properties to a component

Running JavaScript code for the iframe

Tips for executing a .exe file in stealth mode using JavaScript?

I am looking to extract only the pairs from the given array, which is represented as `pairsByIndexRaw = [[0, 3], [1, 2], [2, 1], null, [1], false, "whoops"];`

Ways to verify that window.open is being invoked from a React component

Develop an array of unique objects with multiple dimensions, ensuring no duplicates are included

Utilizing highcharts to visualize non-linear time data pulled from a CSV file

Iterating through a series of Axios requests nested within each other to handle pagination in an

What is the resolution if I need to utilize a property that is untyped?

Creating a dynamic 3D camera view in three.js for navigating around the scene

Occurrences repeating several times following the incorporation of fresh content into the DOM

What steps should I take to resolve the issue with the error message: "BREAKING CHANGE: webpack < 5 previously included polyfills for node.js core modules by default"?

jQuery breaks when working with ASP.NET forms

Update a specific form data field within an Angular application

Error message "Uncaught TypeError: Unable to read property 'defaultView' of undefined" was encountered while using Google Maps

Use setTimeout and setInterval with the initial input without parentheses or double quotation marks

Using jQuery to toggle between open and closed states upon clicking