Read a nested value by dotted path

Half-loaded API responses are the normal case, not the exception. Reaching into one blindly throws "cannot read property of undefined" — and optional chaining does not help when the path itself is data, such as a column key in a config-driven table.

Implement getPath(source, path, fallback). path is a string of segments separated by dots, like "user.profile.name". Walk the segments in order, reading each one as a property. Numeric segments read array indices, so "items.0.id" works. If at any point the current value is null or undefined and there are still segments left, stop and return fallback. If the value you finally arrive at is undefined, also return fallback. fallback defaults to null when not supplied. Falsy values that genuinely exist, such as 0, false and "", are returned as they are, not replaced by the fallback.

getPath({ user: { profile: { name: "Ada" } } }, "user.profile.name");
// "Ada"

getPath({ items: [{ id: 7 }] }, "items.0.id");  // 7 — numeric segments read indices
getPath({ a: 1 }, "a.b.c", "none");             // "none" — broken path yields fallback
getPath({ a: { b: 0 } }, "a.b", "fallback");    // 0 — real falsy values survive