xsheetjs/bits/61_fcommon.js

/* TODO: it will be useful to parse the function str */
var rc_to_a1 = (function(){
	var rcregex = /(^|[^A-Za-z])R(\[?)(-?\d+|)\]?C(\[?)(-?\d+|)\]?/g;
	var rcbase;
	function rcfunc($$,$1,$2,$3,$4,$5) {
		var R = $3.length>0?parseInt($3,10)|0:0, C = $5.length>0?parseInt($5,10)|0:0;
		if(C<0 && $4.length === 0) C=0;
		var cRel = false, rRel = false;
		if($4.length > 0 || $5.length == 0) cRel = true; if(cRel) C += rcbase.c; else --C;
		if($2.length > 0 || $3.length == 0) rRel = true; if(rRel) R += rcbase.r; else --R;
		return $1 + (cRel ? "" : "$") + encode_col(C) + (rRel ? "" : "$") + encode_row(R);
	}
	return function rc_to_a1(fstr, base) {
		rcbase = base;
		return fstr.replace(rcregex, rcfunc);
	};
})();

/* TODO actually parse the formula */
function shift_formula_str(f/*:string*/, delta/*:Cell*/)/*:string*/ {
	return f.replace(/(^|[^A-Z0-9])([$]?)([A-Z]+)([$]?)(\d+)/g, function($0, $1, $2, $3, $4, $5, off, str) {
		return $1+($2=="$" ? $2+$3 : encode_col(decode_col($3)+delta.c))+($4=="$" ? $4+$5 : encode_row(decode_row($5) + delta.r));
	});
}

function shift_formula_xlsx(f/*:string*/, range/*:string*/, cell/*:string*/)/*:string*/ {
	var r = decode_range(range), s = r.s, c = decode_cell(cell);
	var delta = {r:c.r - s.r, c:c.c - s.c};
	return shift_formula_str(f, delta);
}