Summary

Using const enum in .d.ts files breaks compilation with --isolatedModules. Instead, normal enums have been used where a corresponding object exists at runtime. PaperSize does not exist at runtime, and so has been left as const enum for backwards compatibility.

This also adds a declaration for ErrorValue since it exists at runtime but had no TS definition. This does result in some duplication with CellErrorValue, but changing CellErrorValue to use ErrorValue would be a breaking change.

A comparable fix and explanation for the problem with using const enum can be found at chalk/chalk#296, and some further explanation at https://ncjamieson.com/dont-export-const-enums/ and this comment.

Test plan

I created a small project to test this while making changes. Example file:

import { ValueType, CellModel } from 'exceljs';

let vt: ValueType = ValueType.Date;
const vtString = ValueType.String;

export const cm1: Partial<CellModel> = { type: vt };
export const cm2: Partial<CellModel> = { type: vtString };
export const cm3: Partial<CellModel> = { type: ValueType.Boolean };

Before this PR:

• No errors with isolatedModules: false
• Errors with isolatedModules: true

With this PR:

• No errors with isolatedModules: false
• No errors with isolatedModules: true