OS X 10.10 (Yosemite) definitions of the basic script editing functions used in iOS Drafts 4

DraftsFunctions_ScriptEditor.js

// Ver 0.4 Rob Trew 
// Library for using OSX Yosemite Script Editor scripts
// written in an idiom compatible with FoldingText, Drafts, 1Writer, TextWell
// In iOS Drafts 4 scripts, the header is simply:
//	var drafts = this;
// For headers for FoldingText and other editors, see:
// See: http://support.foldingtext.com/t/writing-scripts-which-run-on-both-foldingtext-and-ios-drafts-4/652/7

// Call functions, after this header, with the prefix:
//		drafts.
// e.g.
//		var drafts = Library('DraftsSE');
//		var dctSelnRange = drafts.getSelectedRange(),
//			iFrom = dctSelnRange[0],
//			iTo = iFrom + dctSelnRange[1];

// These functions are intended to be compatible with Agile Tortoise's Drafts documentation at:
// https://agiletortoise.zendesk.com/hc/en-us/articles/202465564-Script-Keys

// getText()                               getSelectedLineRange()
// setText(string)                         getSelectedRange()
// getSelectedText()                       setSelectedRange(start, length)
// setSelectedText(string)                 getClipboard()
// getTextInRange(start, length)           setClipboard(string)
// setTextInRange(start, length, string)

// Installation: Save this as a compiled .scpt to ~/Library/Script Libraries/DraftsSE.scpt
// and then invoke in other scripts as above, through the JXA Library object.

var appSE = Application("Script Editor"),
	lstDocs = appSE.documents(),
	oDoc = lstDocs.length ? lstDocs[0] : null;

appSE.includeStandardAdditions = true;
appSE.activate();

function getText() {
	if (oDoc) return oDoc.text();
}

function setText(strText) {
	if (oDoc) oDoc.text = strText;
}

function getSelectedText() {
	if (oDoc) return oDoc.selection.contents();
}

function setSelectedText(strText) {
	if (oDoc) oDoc.selection.contents = strText;
}

function getTextInRange(iStart, iLength) {
	if (oDoc) return oDoc.text().substring(iStart, iStart + iLength);
}

function setTextInRange(iStart, iLength, strText) {
	if (oDoc) { // record the existing selection coordinates
		var lngDelta = (strText.length - iLength) - 2,
			oSeln = oDoc.selection, dct = oSeln.characterRange(),
			iFrom = dct.x, iTo = dct.y;

		try { // use the selection to edit elsewhere, then restore with any adjustment
			oDoc.selection = oDoc.text.characters.slice(iStart, iStart + iLength);
			oSeln.contents = strText;
			oDoc.selection = oDoc.text.characters.slice(
				(iStart < iFrom) ? iFrom + lngDelta : iFrom,
				((iStart + iLength) < iTo) ? iTo + lngDelta : iTo
			);
		} catch (e) {}
	}
}

function getSelectedLineRange() {
	// works, but let me know if you see a shorter route :-)
	var dct, strFull, iFrom, iTo, lngChars;
	if (oDoc) {
		dct = oDoc.selection.characterRange();
		strFull = oDoc.text();
		lngChars = strFull.length;
		iFrom = dct.x;
		while (iFrom--)
			if (strFull[iFrom] === '\n') break;
		iFrom += 1;
		iTo = dct.y - 1;
		while (iTo++ < lngChars)
			if (strFull[iTo] === '\n') break;
		return [iFrom, (iTo - iFrom)];
	}
}

function getSelectedRange() {
	var dct, iFrom, iTo;
	if (oDoc) {
		dct = oDoc.selection.characterRange();
	}
	iFrom = dct.x;
	iTo = dct.y;
	return [iFrom, iTo - iFrom];
}

function setSelectedRange(iStart, iLength) {
	if (oDoc) {
		oDoc.selection = oDoc.text.characters.slice(iStart, iStart + iLength);
	}
}

function getClipboard() {
	return appSE.theClipboard();
}

function setClipboard(strText) {
	appSE.setTheClipboardTo(strText);
}