How can I send an email with an attachment from the editing screen?

$p.ex.sendMailWithAttachments = function () {
    const toString = 'To:';
    const ccString = 'Cc:';
    const bccString = 'Bcc:';
    const titleString = 'Subject';
    const bodyString = 'Body';
    const mailFormaterElementName = 'Email format';
    const errorFormChanged = 'Press the update button to save the latest record contents before sending';
    const errorGetMail = 'Failed to get email data';
    const errorSendMail = 'Failed to send email';
    const errorSelectedMailFormat = 'Failed to get selected email format data/nProgress status has not changed, please contact sales support';

    let postAttachmentsHash = [];

    if ($p.formChanged == 'undefined' || $p.formChanged) {
        alert(errorFormChanged);
        return;
    }

    if (window.confirm('Send email with the following content')) {

        // Get data for each column 
        let to = $p.getControl(toString).val();
        let cc = $p.getControl(ccString).val();
        let bcc = $p.getControl(bccString).val();
        let title = $p.getControl(titleString).val();
        let body = $p.getControl(bodyString).val();
        let attachments = [];
        let id = $p.id();
        let apiSendMailUrl = $p.apiSendMailUrl(id);
        let isOkResponseData = function(data) {
            let isOk = true;
            if(data == null || data == undefined 
                || data.Response == null || data.Response == undefined 
                || data.Response.Data[0] == null || data.Response.Data[0] == undefined) {
                isOk = false;
            }
            return isOk;
        }
        let isEmpty = function(str) {
            let isEmpty = false;
            if(str == null || str == undefined || str.trim().length <= 0) {
                isEmpty = true;
            }
            return isEmpty;
        }
        $p.apiGet({
            'id': id,
            'done': function (data) {
                if (!isOkResponseData(data)) {
                    alert(errorGetMail);
                    return;
                }
                // Define the column to store the attachments to be attached to the email
                let AttachmentsA = data.Response.Data[0].AttachmentsHash.AttachmentsA;
                let attachmentList = AttachmentsA;

                let createAttachments = async function () {
                    return new Promise((attachmentsResolve, attachmentsReject) => {
                        if (attachmentList.length == 0) {
                            attachmentsResolve();
                        }
                        try {
                            (async () => {
                                for (let i = 0; i < attachmentList.length; i++) {
                                    await new Promise((getResolve, reject) => {
                                        postAttachmentsHash[i] = {
                                            'Guid': attachmentList[i].Guid,
                                            'Deleted': 1,
                                        };
                                        // The path of the url variable below will vary depending on your environment, so please change it as appropriate.
                                        let url = '/binaries/' + attachmentList[i].Guid + '/download';
                                        let xhr = new XMLHttpRequest();
                                        xhr.open('GET', url, true);
                                        xhr.setRequestHeader('Content-Type','application/json');
                                        xhr.responseType = 'arraybuffer';
                                        xhr.onload = function (oEvent) {
                                            if (xhr.readyState == 4 && xhr.status == 200) {
                                                let bytes = new Uint8Array(xhr.response);
                                                let binaryString = '';
                                                for (let i = 0; i < bytes.byteLength; i++) {
                                                    binaryString += String.fromCharCode(bytes[i]);
                                                }
                                                let base64 = window.btoa(binaryString);
                                                let obj = {};
                                                obj.Name = attachmentList[i].Name;
                                                obj.Base64 = base64;
                                                obj.ContentType = xhr.getResponseHeader('content-type');
                                                attachments[i] = obj;
                                                getResolve();
                                                if (i == attachmentList.length - 1) {
                                                    attachmentsResolve();
                                                }
                                            }
                                        }
                                        xhr.send();
                                    });
                                }
                            })();
                        } catch (error) {
                            attachmentsReject(error);
                        }
                    })
                };

                createAttachments().then(function (value) {
                    let postData = {
                        To: to,
                        Cc: cc,
                        Bcc: bcc,
                        Title: isEmpty(title) ? ' ' : title,
                        Body: isEmpty(body) ? ' ' : body,
                        Attachments: attachments
                    };
                    console.log(postData);

                    $.ajax({
                        url: apiSendMailUrl,
                        type: 'post',
                        async: false,
                        cache: false,
                        data: JSON.stringify(postData),
                        contentType: 'application/json',
                        dataType: 'json'
                    })
                        .done(function (json, textStatus, jqXHR) {
                        })
                        .fail(function (jqXHR, textStatus, errorThrown) {
                            alert(errorSendMail);
                        })
                        .always(function () {
                        })
                })
            },
            'fail': function (data) {
                alert(errorGetMail);
            },
            'always': function (data) {
            },
            'async': false
        });
    }
}

// Execute processing when the send email button is pressed
$(document).on('click', "#SendOutgoingMail", function () {
    $p.ex.sendMailWithAttachments();
})