I have a Vue application which need to upload images on server like FormData. As I found out if image is too big Javascipt accidentally rotate the image by 90°. I dont understand it. There is not command to make any changes on image. This is the code:

uploadFiles(files) {
        this.validateUploadFiles(files);

        if( this.uploadErrors?.length ) return;

        this.loading = true;

        const timestamp = Date.now();
        files.forEach( (file, index) => {
            const fileReader = new FileReader();
            fileReader.readAsDataURL(file);

            fileReader.onload = () => {
                const image = new Image();
                image.src = fileReader.result;

                image.onload = async () => {
                    const formData = new FormData();
                    formData.append("file", file);
                    formData.append("index", index);
                    formData.append("timestamp", timestamp);  // This is cause we need to delete prev old remaining files.

                    try {
                        const result = await this.$api.media.uploadCampaignPdfExportMedia( this.campaignId, formData );
                        this.uploadSuccess.push(result.data.fileName);
                    } catch ( error ) {
                        console.log(error);
                        this.uploadErrors.push( this.$t("campaign.upload.error.upload_failed", {name: file.name}) );
                    }
                };
            };
        });
        this.loading = false;
    },

I dont understand what happened there. Can somebody tell me please what is going on?