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# @fastify/merge-json-schemas [](https://github.com/fastify/merge-json-schemas/actions/workflows/ci.yml) [](https://www.npmjs.com/package/@fastify/merge-json-schemas) [](https://github.com/neostandard/neostandard) __merge-json-schemas__ is a JavaScript library that builds a logical product (AND) for multiple [JSON schemas](https://json-schema.org/draft/2020-12/json-schema-core#name-introduction). - [Installation](#installation) - [Usage](#usage) - [API](#api) - [mergeSchemas(schemas, options)](#mergeschemasschemas-options) - [resolvers](#resolvers) - [defaultResolver](#defaultresolver) - [License](#license) <a name="installation"></a> ## Installation ```bash npm i @fastify/merge-json-schemas ``` <a name="usage"></a> ## Usage ```javascript const assert = require('node:assert') const { mergeSchemas } = require('@fastify/merge-json-schemas'); const schema1 = { $id: 'schema1', type: 'object', properties: { foo: { type: 'string', enum: ['foo1', 'foo2'] }, bar: { type: 'string', minLength: 3 } } } const schema2 = { $id: 'schema1', type: 'object', properties: { foo: { type: 'string', enum: ['foo1', 'foo3'] }, bar: { type: 'string', minLength: 5 } }, required: ['foo'] } const mergedSchema = mergeSchemas([schema1, schema2]) assert.deepStrictEqual(mergedSchema, { $id: 'schema1', type: 'object', properties: { foo: { type: 'string', enum: ['foo1'] }, bar: { type: 'string', minLength: 5 } }, required: ['foo'] }) ``` <a name="api"></a> ## API <a name="merge-schemas"></a> #### mergeSchemas(schemas, options) Builds a logical conjunction (AND) of multiple [JSON schemas](https://json-schema.org/draft/2020-12/json-schema-core#name-introduction). - `schemas` __\<objects[]\>__ - list of JSON schemas to merge - `options` __\<object\>__ - optional options - `resolvers` __\<object\>__ - custom resolvers for JSON schema keywords. Each key is the name of a JSON schema keyword. Each value is a resolver function. See [keywordResolver](#keywordresolver-keyword-values-mergedschema-parentschemas-options) - `defaultResolver` __\<function\>__ - custom default resolver for JSON schema keywords. See [keywordResolver](#keywordresolver-keyword-values-mergedschema-parentschemas-options) - `onConflict` __\<string\>__ - action to take when a conflict is found. Used by the default `defaultResolver`. Default is `throw`. Possible values are: - `throw` - throws an error multiple different schemas for the same keyword are found - `ignore` - do nothing if multiple different schemas for the same keyword are found - `first` - use the value of the first schema if multiple different schemas for the same keyword are found #### resolvers A list of default resolvers that __merge-json-schema__ uses to merge JSON schemas. You can override the default resolvers by passing a list of custom resolvers in the `options` argument of `mergeSchemas`. See [keywordResolver](#keywordresolver-keyword-values-mergedschema-parentschemas-options). #### defaultResolver A default resolver that __merge-json-schema__ uses to merge JSON schemas. Default resolver is used when no custom resolver is defined for a JSON schema keyword. By default, the default resolver works as follows: - If only one schema contains the keyword, the value of the keyword is used as the merged value - If multiple schemas contain the exact same value for the keyword, the value of the keyword is used as the merged value - If multiple schemas contain different values for the keyword, it throws an error #### keywordResolver (keyword, values, mergedSchema, parentSchemas, options) __merge-json-schema__ uses a set of resolvers to merge JSON schemas. Each resolver is associated with a JSON schema keyword. The resolver is called when the keyword is found in the schemas to merge. The resolver is called with the following arguments: - `keyword` __\<string\>__ - the name of the keyword to merge - `values` __\<any[]\>__ - the values of the keyword to merge. The length of the array is equal to the number of schemas to merge. If a schema does not contain the keyword, the value is `undefined` - `mergedSchema` __\<object\>__ - an instance of the merged schema - `parentSchemas` __\<object[]\>__ - the list of parent schemas - `options` __\<object\>__ - the options passed to `mergeSchemas` The resolver must set the merged value of the `keyword` in the `mergedSchema` object. __Example:__ resolver for the `minNumber` keyword. ```javascript function minNumberResolver (keyword, values, mergedSchema) { mergedSchema[keyword] = Math.min(...values) } ``` <a name="license"></a> ## License Licensed under [MIT](./LICENSE).