The most common schema used in JavaScript is JSON Schema (json-schema.org). To use it, you first define a schema written in JSON, and then use a schema validation library to compare the object of interest with the schema to see if they match.
But before we explain the syntax of JSON Schema, let's take a look at two major JavaScript libraries that support schema validation while not using JSON Schema:
- joi (https://github.com/hapijs/joi) allows you to define requirements in a composable, chainable manner, which means that the code is very readable. It has over 9,000 stars on GitHub and is depended on by over 94,000 repositories and 3,300 packages:
const schema = Joi.object().keys({ username: Joi.string().alphanum().min(3).max(30).required(), ...
