Order a dependency list

A bundler decides which module to evaluate first, a migration runner decides which migration to apply first, a design-token pipeline decides which theme layer to compile first. All of them answer the same question: given what depends on what, what order works?

Implement topologicalSort(graph). graph is a plain object whose keys are task names and whose values are arrays of the names that task depends on. Return an array of names in which every task appears after all of its dependencies. A name that appears only inside a dependency array, never as a key, is treated as a task with no dependencies of its own and must still appear in the result. An empty object returns an empty array. You may assume the input has no cycles.

So the answer is deterministic, use this exact walk: go through Object.keys(graph) in order; for each name not yet added, first recurse into its dependencies in array order, then append the name itself.

topologicalSort({ c: ["b"], b: ["a"], a: [] });
// ["a", "b", "c"]

topologicalSort({ d: ["b", "c"], b: ["a"], c: ["a"], a: [] });
// ["a", "b", "c", "d"] — the diamond flattens cleanly

topologicalSort({ app: ["lodash"] });
// ["lodash", "app"] — a dependency that's not a key is still included