JavaScript Optional Chaining: Safe Reads and Its Limits

The task

Read a missing contact’s city, compare a continuous chain with a grouped expression and test a present property that is not callable.

Runnable Node 22 example

const assert = require('node:assert/strict');

const profile = {contact: null};
assert.equal(profile.contact?.address?.city, undefined);
assert.throws(() => (profile.contact?.address).city, TypeError);
const tools = {format: 7};
assert.throws(() => tools.format?.(), TypeError);
assert.equal(tools.missing?.(), undefined);
const ready = {contact: {address: {city: 'Leeds'}}};
assert.equal(ready.contact?.address?.city, 'Leeds');
console.log(String(profile.contact?.address?.city) + ' / ' + ready.contact?.address?.city);

Expected output and explanation

The continuous chain returns undefined when contact is null. Grouping the partial result ends that protected chain; the following .city then tries to read from undefined and throws. The asserted error makes the limit explicit.

The optional call on format also throws because seven is present but not a function. The missing method short-circuits instead. Optional means the nullish value may be absent; it is not a substitute for checking a present value’s type.

Pitfall to check

Optional chaining can conceal a missing required relationship if used everywhere without a data contract. Decide which fields are optional, and report invalid required data rather than silently displaying undefined. It also does not make an undeclared root identifier resolvable.