Adding Attachments to a List Item in Sharepoint

Figuring this out took me longer than I expected it would.  Attachments are not included as a column in a SharePoint list, but are saved in a folder that is named after the id of the item you attached the file to.

The folder can be found in Lists/<ListName>/Attachments/<ItemId>

To add files to a list item on a sharepoint page you will need to include a form to attach a file and give it an ID

<input id=”txtAttachements” type=”file”>

And then in the javascript file include the function

function AddAttachments(itemId){
 var digest = "";
 $.ajax({
 url: "/_api/contextinfo",
 method: "POST",
 headers: {
 "ACCEPT": "application/json;odata=verbose",
 "content-type": "application/json;odata=verbose"
 },
 success: function (data) {
 digest = data.d.GetContextWebInformation.FormDigestValue;
 },
 error: function (data) {
 }
 }).done(function() {
 var fileInput = $('#txtAttachements');
 var fileName = fileInput[0].files[0].name;
 var reader = new FileReader();
 reader.onload = function (e) {
 var fileData = e.target.result;
 var res11 = $.ajax({
 url: "/_api/web/lists/getbytitle('Change Orders')/items("+itemId+")/AttachmentFiles/ add(FileName='" + fileName + "')",
 method: "POST",
 binaryStringRequestBody: true,
 data: fileData,
 processData: false,
 headers: {
 "ACCEPT": "application/json;odata=verbose",
 "X-RequestDigest": digest,
 "content-length": fileData.byteLength
 },
 success: function (data) {
 },
 error: function (data) {
 }
 });
 };
 reader.readAsArrayBuffer(fileInput[0].files[0]);
 });
}

Where

 var fileInput = $('#txtAttachements');

is set to the id of the input to attach the file and in the rest call url:

"/_api/web/lists/getbytitle('Change Orders')/items("+itemId+")/AttachmentFiles/ add(FileName='" + fileName + "')",

Change Orders is set to the name of the list you want to get the item to attach a file to from