JSON Path Query

Config readers, GraphQL resolvers, and tools like jq all need to pull a value out of deeply nested data by a path — user.roles[0], items[*].price. A small query engine turns that string into a walk through the object. The twist over a plain obj.a.b.c lookup is the wildcard *: it doesn't pick one child, it picks all of them, so a single path can produce many results. That's why the answer is always an array.

Implement jsonPathQuery(data, path) supporting dotted keys, array indices (bracket or dotted), and *. See JSONPath for the fuller syntax this simplifies.

Signature

function jsonPathQuery(data, path) {
  // returns an array of every value matching `path`
}

Examples

const data = { users: [{ name: 'A' }, { name: 'B' }], config: { a: 1, b: 2 } };

jsonPathQuery(data, 'users[0].name'); // ['A']
jsonPathQuery(data, 'users[*].name'); // ['A', 'B']  — wildcard fans out
jsonPathQuery(data, 'config.*');      // [1, 2]
jsonPathQuery(data, 'users[9].name'); // []           — out of range

Notes

• Segments — split the path on ., and treat [n]/[*] the same as .n/.*. An optional leading $ (root) is ignored.
• Wildcard fans out — * expands to every array element or every object value at that level, so downstream segments run against each.
• Always an array — a wildcard-free path returns 0 or 1 matches; a wildcard path can return many. Return [] for no match.
• No throwing — a missing key, out-of-range index, or descending into a scalar simply contributes no match.