Safe navigation operator (?.) or (!.) and null property paths

Question

In Angular 2 templates safe operator ?. works, but not in component.ts using TypeScript 2.0. Also, safe navigation operator (!.) doesn

Answer 1

A new library called ts-optchain provides this functionality, and unlike lodash' solution, it also keeps your types safe, here is a sample of how it is used (taken from the readme):

import { oc } from 'ts-optchain';

interface I {
  a?: string;
  b?: {
    d?: string;
  };
  c?: Array<{
    u?: {
      v?: number;
    };
  }>;
  e?: {
    f?: string;
    g?: () => string;
  };
}

const x: I = {
  a: 'hello',
  b: {
    d: 'world',
  },
  c: [{ u: { v: -100 } }, { u: { v: 200 } }, {}, { u: { v: -300 } }],
};

// Here are a few examples of deep object traversal using (a) optional chaining vs
// (b) logic expressions. Each of the following pairs are equivalent in
// result. Note how the benefits of optional chaining accrue with
// the depth and complexity of the traversal.

oc(x).a(); // 'hello'
x.a;

oc(x).b.d(); // 'world'
x.b && x.b.d;

oc(x).c[0].u.v(); // -100
x.c && x.c[0] && x.c[0].u && x.c[0].u.v;

oc(x).c[100].u.v(); // undefined
x.c && x.c[100] && x.c[100].u && x.c[100].u.v;

oc(x).c[100].u.v(1234); // 1234
(x.c && x.c[100] && x.c[100].u && x.c[100].u.v) || 1234;

oc(x).e.f(); // undefined
x.e && x.e.f;

oc(x).e.f('optional default value'); // 'optional default value'
(x.e && x.e.f) || 'optional default value';

// NOTE: working with function value types can be risky. Additional run-time
// checks to verify that object types are functions before invocation are advised!
oc(x).e.g(() => 'Yo Yo')(); // 'Yo Yo'
((x.e && x.e.g) || (() => 'Yo Yo'))();