How to define global function in TypeScript?

Question

I want to define a global function that is available everywhere, without the need to import the module when used.

This function aims to replace the safe navigation o

Answer 1

global.ts(x) needs just a little tweak to be a valid "global module" (a module with side effects only): remove the export keyword and add some code to augment the global object. You can also provide the global declaration in the same file and remove global.d.ts.

function _s(object: T | null, defaultValue: T = {} as T) : T {
    return object == null
        ? defaultValue
        : object as T;
}

// Global declaration
declare var s: typeof _s;

// Global scope augmentation
var window = window || null;
const _global = (window || global) as any;
_global.s = _s;

To use it, just import the module once, for instance in App.tsx via a global import: import './global';.

Tested with mocha, chai, ts-node:

import { expect } from 'chai';
import './global'; // To do once at app bootstrapping

describe('global s()', () => {
    it('should replace null with empty object', () => {
        const result = s(null);
        expect(result).to.eql({});
    });

    it('should replace undefined with empty object', () => {
        const result = s(undefined);
        expect(result).to.eql({});
    });

    it('should replace null with the given default value', () => {
        const defVal = { def: 'val' };
        const result = s(null, defVal);
        expect(result).to.eql({ def: 'val' });
    });

    it('should preserve defined object', () => {
        const object = { bar: 'a' };
        const result = s(object);
        expect(result).to.eql(object);
    });
});