How-to guides

Recipes for readers who know what they want to do:

• Restructure fields: rename, move, flatten, and nest with pointer pairings.
• Map arrays of objects: each, element reads, and per-field fallbacks.
• Branch on values: choose a shape at runtime with switch.
• Validate output and apply defaults: constraint keywords and default.
• Validate a mapping before you run it: check documents, read the report, gate evaluation.
• Reuse and compose mappings: $id, $ref, and $extend.
• Write a transformer, initializer, or plugin: the three extension interfaces.
• Fetch remote data: the params-then-plugin idiom and the request plugin.
• Handle errors: the envelope, error objects, and throwing plugins.
• Serve mappings over HTTP: the standalone mapper-http image.
• Validate and submit mappings over HTTP: POST /validate and the explicit form.

Every runnable example is executed against the published engine by the site’s test suite.