Template Expressions

Use Handlebars templates to render dynamic text content in workflows. Call this.render() from any BaseWorkflow to interpolate state values, format prompts, and generate dynamic output.

Setup


import { BaseWorkflow, Transition, Workflow } from '@loopstack/common';
 
@Workflow({})
export class MyWorkflow extends BaseWorkflow {
  // this.render() is available from BaseWorkflow — no injection needed
}

Usage


const rendered = this.render(__dirname + '/templates/prompt.md', {
  subject: args.subject,
  items: state.items,
});

Template file (templates/prompt.md):


Write a haiku about {{subject}}.
 
{{#each items}}
 
- {{this.name}}
  {{/each}}

Passing Data

Pass any data as the second argument to this.render():


// Workflow args (from ctx parameter)
const args = ctx.args as { subject: string };
this.render(templatePath, { subject: args.subject });
 
// Workflow state (from state parameter)
this.render(templatePath, { items: state.items, count: state.counter });
 
// Mixed data
this.render(templatePath, {
  prompt: args.prompt,
  history: state.conversationHistory,
  timestamp: new Date().toISOString(),
});

Handlebars Syntax

Variables


Hello {{name}}
Nested: {{user.profile.email}}
Array element: {{items.[0]}}

Conditionals


{{#if isActive}}Welcome back!{{else}}Please log in{{/if}}
{{#unless isBlocked}}Access granted{{/unless}}

Iteration


{{#each items}}
 
- {{this.name}}: {{this.value}}
  {{else}}
  No items found.
  {{/each}}

Context Scoping


{{#with user}}{{name}} ({{email}}){{/with}}

Multi-line Template Example


# Events This Week
 
{{#each events}}
 
- **{{this.summary}}**: {{this.start}} – {{this.end}}
  {{/each}}
 
{{#unless events}}
No events found.
{{/unless}}

When to Use Templates

Scenario	Approach
LLM prompts with variables	`this.render(templatePath, data)`
Simple string interpolation	Template literals in TypeScript
Complex multi-line content	Handlebars template file
Prompts with iteration/conditionals	Handlebars with `#each`, `#if`

YAML UI Config

YAML widget configuration uses transition values that reference method names and enabledWhen for conditional visibility. These are not template expressions — they are static configuration:


ui:
  widgets:
    - widget: prompt-input
      enabledWhen: [waiting_for_user]
      options:
        transition: userMessage

Registry References

prompt-example-workflow — Uses this.render() for Handlebars prompt templates
meeting-notes-example-workflow — Uses templates for structured note rendering