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JSON schema validator

Q: JSON schema validator

**Target Audience:** Engineers preparing for practical JavaScript coding interviews. **Difficulty:** Medium > **How to read this doc:** all 5 real validation scenarios below — valid data, a missing field, a wrong type, a below-minimum value, and a bad nested array item — were verified directly, each producing the exact expected error message and path. ## 1. The problem, restated Given a schema describing an object's expected shape (`type`, `required` properties, nested `properties`, array `items`, and a numeric `minimum` constraint), recursively check real data against it, COLLECTING every validation failure found anywhere in the structure — not stopping at the first — with each error reporting the exact field path it applies to. ## 2. Clarifying questions a strong candidate asks | Question | Why it matters | | :--- | :--- | | Stop at first error, or collect all? | Collecting all is the real, more useful convention — a real form/API validator showing only ONE error at a time force

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The problem

Problem, as an interviewer would state it: "Implement a minimal validate(schema, data) supporting a real subset of JSON Schema: type, required, properties, items, and minimum — returning every validation error found, with the exact path to each one."

Examples:

Code

validate({ type: "object", required: ["name"], properties: { name: { type: "string" } } }, { });
// { valid: false, errors: ["$: missing required property \"name\""] }

Clarifying questions expected:

Should validation stop at the FIRST error, or collect every error across the whole structure?
Does each error need to report the exact PATH to the offending field, for real usability?
Which real JSON Schema keywords are actually in scope — the full real spec, or a deliberately small subset?

Code / implementation expected: Yes — real, direct proof across 5 scenarios: fully valid data, a missing required field, a wrong type, a below-minimum number, and an invalid nested array item type.

js-coding
utility
algorithm

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Solution

Target Audience: Engineers preparing for practical JavaScript coding interviews. Difficulty: Medium

How to read this doc: all 5 real validation scenarios below — valid data, a missing field, a wrong type, a below-minimum value, and a bad nested array item — were verified directly, each producing the exact expected error message and path.

1. The problem, restated

Given a schema describing an object's expected shape (type, required properties, nested properties, array items, and a numeric minimum constraint), recursively check real data against it, COLLECTING every validation failure found anywhere in the structure — not stopping at the first — with each error reporting the exact field path it applies to.

2. Clarifying questions a strong candidate asks

Question	Why it matters
Stop at first error, or collect all?	Collecting all is

The solution is hidden so you can try first

6 min read · 9 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

JavaScriptReal, direct proof: the validator correctly reports the exact error and path across 5 real scenarios, including a nested array item type mismatch

Practice

Discussion

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