script fails in orientating image and returning the new one: undefined

Question

I was looking here for a method to orientate images client side using javascript. I found something and finally got this script. It seems the image is being passed correctly but then the result of ctx.drawImage(img, 0, 0); is undefined and I don't get why. I just need the function to return the new image as base64 so that I can handle properly for inserting in the dom. I am not sure I am returning it correctly either but there's a prior problem where as stated drawImage is returning undefined, it seems like it is trying a route undefined:1 GET http://myproject.dev/model/undefined 404 (Not Found) probably I'm missing something stupid.

the event part

$(document).ready(function() {
    $('#modelpic').on("change", function () {

        //shows image preview in DOM
        var files = !!this.files ? this.files : [];

        if (!files.length || !window.FileReader) return; // no file selected, or no FileReader support

        if (/^image/.test( files[0].type)){ // only image file
            var reader = new FileReader(); // instance of the FileReader

            reader.readAsDataURL(this.files[0]); // read the local file

            reader.onloadend = function(){ // show image in div

                var base64img = this.result;

                var exif = EXIF.readFromBinaryFile(base64ToArrayBuffer(this.result));
                var srcOrientation = exif.Orientation;

                var img = resetOrientation(base64img, srcOrientation);

                $('#imagePreview').show().html('<img id="theImage" src="' + img + '" class="img-fluid" alt="Your Image" />');

            }
        }
    })
});

The function that takes care of orientation

function resetOrientation(srcBase64, srcOrientation) {

    var img = new Image();

    img.onload = function() {
        var width = img.width,
            height = img.height,
            canvas = document.createElement('canvas'),
            ctx = canvas.getContext("2d");

        console.log(ctx);

        // set proper canvas dimensions before transform & export
        if ([5,6,7,8].indexOf(srcOrientation) > -1) {
            canvas.width = height;
            canvas.height = width;
        } else {
            canvas.width = width;
            canvas.height = height;
        }

        // transform context before drawing image
        switch (srcOrientation) {
            case 2: ctx.transform(-1, 0, 0, 1, width, 0); break;
            case 3: ctx.transform(-1, 0, 0, -1, width, height ); break;
            case 4: ctx.transform(1, 0, 0, -1, 0, height ); break;
            case 5: ctx.transform(0, 1, 1, 0, 0, 0); break;
            case 6: ctx.transform(0, 1, -1, 0, height , 0); break;
            case 7: ctx.transform(0, -1, -1, 0, height , width); break;
            case 8: ctx.transform(0, -1, 1, 0, 0, width); break;
            default: ctx.transform(1, 0, 0, 1, 0, 0);
        }

        // draw image
        ctx.drawImage(img, 0, 0);

        // export base64
        return img;
    };

    img.src = srcBase64;
};

The function to convert base64 to array for EXIF checking.

function base64ToArrayBuffer (base64) {
    base64 = base64.replace(/^data:([^;]+);base64,/gmi, '');
    var binaryString = window.atob(base64);
    var len = binaryString.length;
    var bytes = new Uint8Array(len);
    for (var i = 0; i < len; i++) {
        bytes[i] = binaryString.charCodeAt(i);
    }
    return bytes.buffer;
}

Answer 1

1. you are not returning anything inside "resetOrientation"
2. Looks like you tried to return canvas element, wich is still bad as it won't work inside src=""
3. img.onload is async

I think this is the way to go (although not tested)

function resetOrientation(srcBase64, srcOrientation) {
    return new Promise(function(resolve, reject){

      var img = new Image();

    img.onload = function() {
        var width = img.width,
            height = img.height,
            canvas = document.createElement('canvas'),
            ctx = canvas.getContext("2d");

        console.log(ctx);

        // set proper canvas dimensions before transform & export
        if ([5,6,7,8].indexOf(srcOrientation) > -1) {
            canvas.width = height;
            canvas.height = width;
        } else {
            canvas.width = width;
            canvas.height = height;
        }

        // transform context before drawing image
        switch (srcOrientation) {
            case 2: ctx.transform(-1, 0, 0, 1, width, 0); break;
            case 3: ctx.transform(-1, 0, 0, -1, width, height ); break;
            case 4: ctx.transform(1, 0, 0, -1, 0, height ); break;
            case 5: ctx.transform(0, 1, 1, 0, 0, 0); break;
            case 6: ctx.transform(0, 1, -1, 0, height , 0); break;
            case 7: ctx.transform(0, -1, -1, 0, height , width); break;
            case 8: ctx.transform(0, -1, 1, 0, 0, width); break;
            default: ctx.transform(1, 0, 0, 1, 0, 0);
        }

        // draw image
        ctx.drawImage(img, 0, 0);

        // export base64
        resolve(canvas.toDataURL())
    };

    img.src = srcBase64;

    })

};

and then

$(document).ready(function() {
    $('#modelpic').on("change", function () {

        //shows image preview in DOM
        var files = !!this.files ? this.files : [];

        if (!files.length || !window.FileReader) return; // no file selected, or no FileReader support

        if (/^image/.test( files[0].type)){ // only image file
            var reader = new FileReader(); // instance of the FileReader

            reader.readAsDataURL(this.files[0]); // read the local file

            reader.onloadend = function(){ // show image in div

                var base64img = this.result;

                var exif = EXIF.readFromBinaryFile(base64ToArrayBuffer(this.result));
                var srcOrientation = exif.Orientation;

                resetOrientation(base64img, srcOrientation).then((img)=>{
                  $('#imagePreview').show().html('<img id="theImage" src="' + img + '" class="img-fluid" alt="Your Image" />');
                })



            }
        }
    })
});