expression

Generate Kibana Expression

Create custom Expression Functions and/or Renderers that integrate with Kibana's expression pipeline (Canvas, Lens, Dashboard). Ask the user for:

1. Function or Renderer? Are they creating an expression function, a renderer, or both?
2. Function name (snake_case, e.g. my_metric_calc)
3. What it does (description of the transformation or computation)
4. Input type — what data does it receive from the previous function in the pipeline? (datatable, number, string, null, kibana_context)
5. Arguments — named parameters with types and defaults
6. Output type — what data does it produce? (datatable, number, string, render, custom type)
7. For renderers: What does it visually display? (chart, metric, table, custom visualization)
8. Server or browser? Does the function need server-side access (ES queries) or is it browser-only?

Generation Steps

1. Create the expression files:

   common/expressions/          # Functions that work on both server and browser
   ├── index.ts
   ├── my_function.ts           # Expression function definition
   └── types.ts                 # Custom expression types
   public/expression_renderers/ # Renderers (browser-only)
   ├── index.ts
   └── my_renderer.tsx          # Expression renderer
   

2. For an Expression Function:

   • Define the function using ExpressionFunctionDefinition
   • Specify name, help, args, inputTypes, type (output)
   • Implement fn(input, args, context) — the transformation logic
   • Register in setup() via expressions.registerFunction(myFunction)

3. For an Expression Renderer:

   • Define the renderer using ExpressionRenderDefinition
   • Specify name, displayName, help, reuseDomNode
   • Implement render(domNode, config, handlers) — mounts the visualization
   • Call handlers.done() when rendering is complete
   • Register in setup() via expressions.registerRenderer(myRenderer)