Updated standalone documentation and add new examples

docs/standalone.md

@@ -2,83 +2,241 @@
 
 [[toc]]
 
-Ajv supports generating standalone modules with exported validation function(s), with one default export or multiple named exports, that are pre-compiled and can be used without Ajv. It is useful for several reasons:
+Ajv supports generating standalone validation functions from JSON Schemas at compile/build time. These functions can then be used during runtime to do validation without initialising Ajv. It is useful for several reasons:
 
 - to reduce the browser bundle size - Ajv is not included in the bundle (although if you have a large number of schemas the bundle can become bigger - when the total size of generated validation code is bigger than Ajv code).
 - to reduce the start-up time - the validation and compilation of schemas will happen during build time.
 - to avoid dynamic code evaluation with Function constructor (used for schema compilation) - when it is prohibited by the browser page [Content Security Policy](./security.md#content-security-policy).
 
-This functionality in Ajv v7 supersedes deprecated package ajv-pack that can be used with Ajv v6. All schemas, including those with recursive references, formats and user-defined keywords are supported, with few [limitations](#configuration-and-limitations).
+This functionality in Ajv v7 supersedes the deprecated package ajv-pack that can be used with Ajv v6. All schemas, including those with recursive references, formats and user-defined keywords are supported, with few [limitations](#configuration-and-limitations).
 
-## Usage with CLI
+## Two-step process 
 
-In most cases you would use this functionality via [ajv-cli](https://github.com/ajv-validator/ajv-cli) (>= 4.0.0) to generate module that exports validation function.
+The **first step** is to **generate** the standalone validation function code. This is done at compile/build time of your project and the output is a generated JS file. The **second step** is to **use** the generated JS validation function.
 
+There are two methods to generate the code, using either the Ajv CLI or the Ajv JS library. There are also a few different options that can be passed when generating code. Below is just a highlight of a few options:
+
+- Set the `code.source` (JS) value to true or use the `compile` (CLI) command to generate standalone code.
+- The standalone code can be generated in either ES5 or ES6, it defaults to ES6. Set the `code.es5` (JS) value to true or pass the `--code-es5` (CLI) flag to true if you want ES5 code.
+- The standalone code can be generated in either CJS (module.export & require) or ESM (exports & import), it defaults to CJS. Set the `code.esm` (JS) value to true or pass the `--code-esm` (CLI) flag if you want ESM exported code.
+
+Note that the way the function is exported, differs if you are exporting a single or multiple schemas. See examples below.
+
+### Generating function(s) using CLI
+
+In most cases you would use this functionality via [ajv-cli](https://github.com/ajv-validator/ajv-cli) (>= 4.0.0) to generate the standalone code that exports the validation function. See [ajv-cli](https://github.com/ajv-validator/ajv-cli#compile-schemas) docs and the [cli options](https://github.com/ajv-validator/ajv-cli#ajv-options) for additional information.
+
+#### Using the defaults - ES6 and CJS exports
 ```sh
 npm install -g ajv-cli
 ajv compile -s schema.json -o validate_schema.js
 ```
 
-`validate_schema.js` will contain the module exporting validation function that can be bundled into your application.
-
-See [ajv-cli](https://github.com/ajv-validator/ajv-cli) docs for additional information.
-
-## Usage from code
+### Generating using the JS library
 
+Install the package, version >= v7.0.0: 
 ```sh
 npm install ajv
 ```
 
+#### Generating functions(s) for a single schema using the JS library - ES6 and CJS exports
+
 ```javascript
-const Ajv = require("ajv") // version >= v7.0.0
-const ajv = new Ajv({code: {source: true}}) // this option is required to generate standalone code
+const fs = require("fs")
+const path = require("path")
+const Ajv = require("ajv")
 const standaloneCode = require("ajv/dist/standalone").default
 
 const schema = {
-  $id: "https://example.com/object.json",
+  $id: "https://example.com/bar.json",
+  $schema: "http://json-schema.org/draft-07/schema#",
   type: "object",
   properties: {
-    foo: {
-      type: "string",
-      pattern: "^[a-z]+$",
-    },
+    bar: {type: "string"},
   },
+  "required": ["bar"]
 }
 
-// 1. generate module with a single default export (CommonJS and ESM compatible):
+// The generated code will have a default export:
+// `module.exports = <validateFunctionCode>;module.exports.default = <validateFunctionCode>;`
+const ajv = new Ajv({code: {source: true}})
 const validate = ajv.compile(schema)
 let moduleCode = standaloneCode(ajv, validate)
 
-// 2. pass map of schema IDs to generate multiple exports,
-// it avoids code duplication if schemas are mutually recursive or have some share elements:
-let moduleCode = standaloneCode(ajv, {
-  validateObject: "https://example.com/object.json",
-})
+// Now you can write the module code to file
+fs.writeFileSync(path.join(__dirname, "../consume/validate-cjs.js"), moduleCode)
+```
+
+#### Generating functions(s) for multiple schemas using the JS library - ES6 and CJS exports
+
+```javascript
+const fs = require("fs")
+const path = require("path")
+const Ajv = require("ajv")
+const standaloneCode = require("ajv/dist/standalone").default
 
-// 3. or generate module with all schemas added to the instance (excluding meta-schemas),
-// export names would use schema IDs (or keys passed to addSchema method):
+const schemaFoo = {
+  $id: "#/definitions/Foo",
+  $schema: "http://json-schema.org/draft-07/schema#",
+  type: "object",
+  properties: {
+    foo: {"$ref": "#/definitions/Bar"}
+  }
+}
+const schemaBar = {
+  $id: "#/definitions/Bar",
+  $schema: "http://json-schema.org/draft-07/schema#",
+  type: "object",
+  properties: {
+    bar: {type: "string"},
+  },
+  "required": ["bar"]
+}
+
+// For CJS, it generates an exports array, will generate
+// `exports["#/definitions/Foo"] = ...;exports["#/definitions/Bar"] = ... ;`
+const ajv = new Ajv({schemas: [schemaFoo, schemaBar], code: {source: true}})
 let moduleCode = standaloneCode(ajv)
 
-// now you can
-// write module code to file
+// Now you can write the module code to file
+fs.writeFileSync(path.join(__dirname, "../consume/validate-cjs.js"), moduleCode)
+```
+
+#### Generating functions(s) for multiple schemas using the JS library - ES6 and ESM exports
+
+```javascript
 const fs = require("fs")
 const path = require("path")
-fs.writeFileSync(path.join(__dirname, "/validate.js"), moduleCode)
+const Ajv = require("ajv")
+const standaloneCode = require("ajv/dist/standalone").default
+
+const schemaFoo = {
+  $id: "#/definitions/Foo",
+  $schema: "http://json-schema.org/draft-07/schema#",
+  type: "object",
+  properties: {
+    foo: {"$ref": "#/definitions/Bar"}
+  }
+}
+const schemaBar = {
+  $id: "#/definitions/Bar",
+  $schema: "http://json-schema.org/draft-07/schema#",
+  type: "object",
+  properties: {
+    bar: {type: "string"},
+  },
+  "required": ["bar"]
+}
 
-// ... or require module from string
-const requireFromString = require("require-from-string")
-const standaloneValidate = requireFromString(moduleCode) // for a single default export
+// For ESM, the export name needs to be a valid export name, it can not be `export const #/definitions/Foo = ...;` so we
+// need to provide a mapping between a valid name and the $id field. Below will generate
+// `export const Foo = ...;export const Bar = ...;`
+// This mapping would not have been needed if the `$ids` was just `Bar` and `Foo` instead of `#/definitions/Foo`
+// and `#/definitions/Bar` respectfully
+const ajv = new Ajv({schemas: [schemaFoo, schemaBar], code: {source: true, esm: true}})
+let moduleCode = standaloneCode(ajv, {
+  "Foo": "#/definitions/Foo",
+  "Bar": "#/definitions/Bar"
+})
+
+// Now you can write the module code to file
+fs.writeFileSync(path.join(__dirname, "../consume/validate-esm.mjs"), moduleCode)
+```
+
+::: warning ESM name mapping
+The ESM version only requires the mapping if the ids are not valid export names. If the $ids were just the
+`Foo` and `Bar` instead of `#/definitions/Foo` and `#/definitions/Bar` then the mapping would not be needed.
+:::
+
+
+## Using the validation function(s)
+
+### Validating a single schemas using the JS library - ES6 and CJS
+
+```javascript
+const Bar = require('./validate-cjs')
+
+const barPass = {
+    bar: "something"
+}
+
+const barFail = {
+    // bar: "something" // <= empty/omitted property that is required
+}
+
+let validateBar = Bar
+if (!validateBar(barPass))
+  console.log("ERRORS 1:", validateBar.errors) //Never reaches this because valid
+
+if (!validateBar(barFail))
+  console.log("ERRORS 2:", validateBar.errors) //Errors array gets logged
+```
+
+### Validating multiple schemas using the JS library - ES6 and CJS
+
+```javascript
+const validations = require('./validate-cjs')
+
+const fooPass = {
+  foo: {
+    bar: "something"
+  }
+}
+
+const fooFail = {
+  foo: {
+    // bar: "something" // <= empty/omitted property that is required
+  }
+}
+
+let validateFoo = validations["#/definitions/Foo"];
+if (!validateFoo(fooPass))
+  console.log("ERRORS 1:", validateFoo.errors); //Never reaches this because valid
+
+if (!validateFoo(fooFail))
+  console.log("ERRORS 2:", validateFoo.errors); //Errors array gets logged
+
+```
+
+### Validating multiple schemas using the JS library - ES6 and ESM
+
+```javascript
+import {Foo, Bar} from './validate-multiple-esm.mjs';
+
+const fooPass = {
+  foo: {
+    bar: "something"
+  }
+}
+
+const fooFail = {
+  foo: {
+    // bar: "something" // bar: "something" <= empty properties
+  }
+}
+
+let validateFoo = Foo;
+if (!validateFoo(fooPass))
+  console.log("ERRORS 1:", validateFoo.errors); //Never reaches here because valid
+
+if (!validateFoo(fooFail))
+  console.log("ERRORS 2:", validateFoo.errors); //Errors array gets logged
 ```
 
+
 ### Requirement at runtime
 
-To run the standalone generated functions, the Ajv package should still be a run-time dependency for most schemas, but generated modules can only depend on code in [runtime](https://github.com/ajv-validator/ajv/tree/master/lib/runtime) folder, so the whole Ajv will not be included in the bundle (or executed) if you require the modules with standalone validation code from your application code.
+One of the main reason for using the standalone mode is to start applications faster to avoid runtime schema compilation. 
+
+The standalone generated functions still has a dependency on the Ajv. Specifically on the code in the [runtime](https://github.com/ajv-validator/ajv/tree/master/lib/runtime) folder of the package. 
+
+Completely isolated validation functions can be generated if desired (won't be for most use cases). Run the generated code through a bundler like ES Build to create completely isolated validation functions that can be imported/required without any dependency on Ajv. This is also not needed if your project is already using a bundler.
 
 ## Configuration and limitations
 
 To support standalone code generation:
 
-- Ajv option `source.code` must be set to `true`
+- Ajv option `code.source` must be set to `true`
 - only `code` and `macro` user-defined keywords are supported (see [User defined keywords](./keywords.md)).
 - when `code` keywords define variables in shared scope using `gen.scopeValue`, they must provide `code` property with the code snippet. See source code of pre-defined keywords for examples in [vocabularies folder](https://github.com/ajv-validator/ajv/blob/master/lib/vocabularies).
 - if formats are used in standalone code, ajv option `code.formats` should contain the code snippet that will evaluate to an object with all used format definitions - it can be a call to `require("...")` with the correct path (relative to the location of saved module):
@@ -93,6 +251,5 @@ const ajv = new Ajv({
     formats: _`require("./my-formats")`,
   },
 })
-```
 
 If you only use formats from [ajv-formats](https://github.com/ajv-validator/ajv-formats) this option will be set by this package automatically.