Decorators

CrystalFlow uses TypeScript decorators to define nodes declaratively. Decorators provide metadata about nodes, inputs, outputs, and properties without cluttering your business logic.

What are Decorators?

Decorators are special annotations that add metadata to classes and properties:

@defineNode({ type: 'math.add', label: 'Add' })
class AddNode extends Node {
  @Input({ type: 'number', label: 'A' })
  a: number = 0;
  
  @Output({ type: 'number', label: 'Result' })
  result: number;
}

Decorators are a TypeScript feature that requires experimentalDecorators: true in your tsconfig.json

@defineNode

The @defineNode decorator registers a node class with CrystalFlow:

@defineNode({
  type: 'category.nodename',
  label: 'Display Name',
  category: 'Category',
  description: 'Optional description'
})
class MyNode extends Node {
  // ...
}

Parameters

type

string

required

Unique identifier for the node type (e.g., 'math.add', 'http.request')Convention: Use dot notation like category.operation

label

string

required

Human-readable name shown in the UI

Example

@defineNode({
  type: 'string.uppercase',
  label: 'To Uppercase',
  category: 'String',
  description: 'Converts a string to uppercase'
})
class UppercaseNode extends Node {
  execute() {
    this.output = this.input.toUpperCase();
  }
}

@Input

The @Input decorator defines an input port on a node:

@Input({
  type: 'string',
  label: 'Message',
  defaultValue: 'Hello',
  required: false,
  description: 'Input message'
})
message: string = 'Hello';

Parameters

type

string

required

Data type of the input: 'string', 'number', 'boolean', 'any', or custom types

label

string

required

Display name for the input port in the UI

defaultValue

any

Default value if no connection is made

required

boolean

default:"false"

Whether this input must be connected or have a value

description

string

Optional description of the input’s purpose

Example

@defineNode({
  type: 'math.power',
  label: 'Power',
  category: 'Math'
})
class PowerNode extends Node {
  @Input({ 
    type: 'number', 
    label: 'Base',
    defaultValue: 2,
    description: 'The base number'
  })
  base: number = 2;

  @Input({ 
    type: 'number', 
    label: 'Exponent',
    defaultValue: 2,
    description: 'The power to raise to'
  })
  exponent: number = 2;

  @Output({ type: 'number', label: 'Result' })
  result: number;

  execute() {
    this.result = Math.pow(this.base, this.exponent);
  }
}

@Output

The @Output decorator defines an output port on a node:

@Output({
  type: 'string',
  label: 'Result',
  description: 'The processed result'
})
result: string;

Parameters

type

string

required

Data type of the output: 'string', 'number', 'boolean', 'any', or custom types

label

string

required

Display name for the output port in the UI

description

string

Optional description of what the output represents

Example

@defineNode({
  type: 'http.request',
  label: 'HTTP Request',
  category: 'Network'
})
class HttpRequestNode extends Node {
  @Output({ 
    type: 'any', 
    label: 'Response',
    description: 'HTTP response data'
  })
  response: any;

  @Output({ 
    type: 'number', 
    label: 'Status Code',
    description: 'HTTP status code'
  })
  statusCode: number;

  @Output({ 
    type: 'any', 
    label: 'Headers',
    description: 'Response headers'
  })
  headers: any;

  async execute() {
    const res = await fetch(this.url);
    this.response = await res.json();
    this.statusCode = res.status;
    this.headers = Object.fromEntries(res.headers.entries());
  }
}

@Property

The @Property decorator defines a static configuration value (not connected to other nodes):

@Property({
  type: 'select',
  label: 'Operation',
  defaultValue: 'add',
  options: [
    { value: 'add', label: 'Add' },
    { value: 'subtract', label: 'Subtract' }
  ],
  description: 'The operation to perform'
})
operation: string = 'add';

Parameters

type

'string' | 'number' | 'boolean' | 'select'

required

The property type

label

string

required

Display label in the properties panel

defaultValue

any

Default value for the property

required

boolean

default:"false"

Whether the property is required

description

string

Description shown in the UI

options

Array<{value: any, label: string}>

Options for select type properties

min

number

Minimum value for number properties

max

number

Maximum value for number properties

step

number

Step increment for number properties

Example

@defineNode({
  type: 'data.filter',
  label: 'Filter Array',
  category: 'Data'
})
class FilterNode extends Node {
  @Property({
    type: 'select',
    label: 'Condition Type',
    defaultValue: 'equals',
    options: [
      { value: 'equals', label: 'Equals' },
      { value: 'contains', label: 'Contains' },
      { value: 'greater', label: 'Greater Than' }
    ]
  })
  conditionType: string = 'equals';

  @Property({
    type: 'string',
    label: 'Field Name',
    defaultValue: 'id',
    description: 'The field to filter by'
  })
  fieldName: string = 'id';

  @Property({
    type: 'number',
    label: 'Max Results',
    defaultValue: 100,
    min: 1,
    max: 1000,
    step: 10
  })
  maxResults: number = 100;

  @Input({ type: 'any[]', label: 'Array' })
  array: any[] = [];

  @Output({ type: 'any[]', label: 'Filtered' })
  filtered: any[];

  execute() {
    // Use properties in logic
    this.filtered = this.array
      .filter(item => this.applyCondition(item))
      .slice(0, this.maxResults);
  }
}

Property vs Input

Key Difference:

@Property = Static configuration in properties panel (not connected)
@Input = Dynamic data flow via connections
@Output = Computed results during execution

class ExampleNode extends Node {
  // Property: Set once in UI, doesn't change
  @Property({ type: 'string', label: 'API Endpoint' })
  endpoint: string = 'https://api.example.com';

  // Input: Receives data from other nodes
  @Input({ type: 'string', label: 'Query' })
  query: string = '';

  // Output: Produces data for other nodes
  @Output({ type: 'any', label: 'Data' })
  data: any;

  async execute() {
    // Use property and input to produce output
    const response = await fetch(`${this.endpoint}?q=${this.query}`);
    this.data = await response.json();
  }
}

Decorator Inheritance

Properties and decorators are inherited from base classes:

// Base class with common properties
class BaseApiNode extends Node {
  @Property({
    type: 'boolean',
    label: 'Enable Logging',
    defaultValue: false
  })
  enableLogging: boolean = false;

  @Property({
    type: 'number',
    label: 'Timeout (ms)',
    defaultValue: 30000
  })
  timeout: number = 30000;
}

// Child class inherits properties
@defineNode({
  type: 'api.users',
  label: 'Fetch Users',
  category: 'API'
})
class FetchUsersNode extends BaseApiNode {
  // Inherits enableLogging and timeout

  @Output({ type: 'any[]', label: 'Users' })
  users: any[];

  async execute() {
    if (this.enableLogging) {
      console.log('Fetching users...');
    }
    // Use inherited timeout property
    // ...
  }
}

TypeScript Configuration

To use decorators, configure your tsconfig.json:

tsconfig.json

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "emitDecoratorMetadata": true,
    "target": "ES2020",
    "module": "ESNext"
  }
}

Don’t forget reflect-metadata!Import reflect-metadata at the top of your entry file:

import 'reflect-metadata';

Best Practices

Use Descriptive Labels

Labels should be clear and concise - they’re shown to users in the UI.

Add Descriptions

Always add descriptions to help users understand what inputs, outputs, and properties do.

Set Sensible Defaults

Provide default values that work out of the box.

Use Type Prefixes

Name node types with category prefixes: math.add, string.uppercase, http.request

Group Related Nodes

Complete Example

Here’s a complete node using all decorators:

import 'reflect-metadata';
import { Node, defineNode, Property, Input, Output } from '@crystalflow/core';

@defineNode({
  type: 'text.replace',
  label: 'Replace Text',
  category: 'Text',
  description: 'Replace occurrences of text in a string'
})
export class ReplaceTextNode extends Node {
  // Property: Configuration
  @Property({
    type: 'boolean',
    label: 'Case Sensitive',
    defaultValue: true,
    description: 'Whether matching should be case sensitive'
  })
  caseSensitive: boolean = true;

  @Property({
    type: 'boolean',
    label: 'Replace All',
    defaultValue: true,
    description: 'Replace all occurrences or just the first'
  })
  replaceAll: boolean = true;

  // Inputs: Dynamic data
  @Input({
    type: 'string',
    label: 'Text',
    required: true,
    description: 'The text to search in'
  })
  text: string = '';

  @Input({
    type: 'string',
    label: 'Find',
    required: true,
    description: 'The text to find'
  })
  find: string = '';

  @Input({
    type: 'string',
    label: 'Replace',
    defaultValue: '',
    description: 'The replacement text'
  })
  replace: string = '';

  // Outputs: Results
  @Output({
    type: 'string',
    label: 'Result',
    description: 'The text with replacements made'
  })
  result: string;

  @Output({
    type: 'number',
    label: 'Count',
    description: 'Number of replacements made'
  })
  count: number;

  // Business logic
  execute() {
    let searchText = this.text;
    let findText = this.find;

    if (!this.caseSensitive) {
      searchText = searchText.toLowerCase();
      findText = findText.toLowerCase();
    }

    if (this.replaceAll) {
      const regex = new RegExp(
        findText.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'),
        this.caseSensitive ? 'g' : 'gi'
      );
      this.result = this.text.replace(regex, this.replace);
      this.count = (this.text.match(regex) || []).length;
    } else {
      const index = searchText.indexOf(findText);
      if (index !== -1) {
        this.result = 
          this.text.slice(0, index) +
          this.replace +
          this.text.slice(index + this.find.length);
        this.count = 1;
      } else {
        this.result = this.text;
        this.count = 0;
      }
    }
  }
}

Next Steps

Creating Custom Nodes

Deep dive into building custom nodes

Property System

Master the property system

Inheritance

Learn about decorator inheritance

Decorators API

Complete decorators API reference

Getting Started

Core Concepts

Guides

Advanced

What are Decorators?

@defineNode

Parameters

Example

@Input

Parameters

Example

@Output

Parameters

Example

@Property

Parameters

Example

Property vs Input

Decorator Inheritance

TypeScript Configuration

Best Practices

Complete Example

Next Steps

Creating Custom Nodes

Property System

Inheritance

Decorators API

Getting Started

Core Concepts

Guides

Advanced

​What are Decorators?

​@defineNode

​Parameters

​Example

​@Input

​Parameters

​Example

​@Output

​Parameters

​Example

​@Property

​Parameters

​Example

​Property vs Input

​Decorator Inheritance

​TypeScript Configuration

​Best Practices

​Complete Example

​Next Steps

Creating Custom Nodes

Property System

Inheritance

Decorators API

What are Decorators?

@defineNode

Parameters

Example

@Input

Parameters

Example

@Output

Parameters

Example

@Property

Parameters

Example

Property vs Input

Decorator Inheritance

TypeScript Configuration

Best Practices

Complete Example

Next Steps