f-strings

f-strings

Template function with conditional expressions and automatic dedentation

f-strings provides a tagged template f that allows you to write readable multi-line strings with embedded if-else conditions and automatic dedentation.

Installation

npm install f-strings

Usage

Use If, Else, and EndIf expressions to include conditional content.

import { f, If, Else, EndIf } from 'f-strings';

const history = [
  { role: 'user', content: 'Hello' },
  { role: 'assistant', content: 'Hi there!' },
];

const question = 'What is the capital of France?';

const prompt = f`
  You are a helpful assistant.

  ${If(history.length)}
  Conversation history:
  ${history.map((msg) => `- ${msg.role}: ${msg.content}`)}
  ${Else}
  No conversation history.
  ${EndIf}

  User question:
  ${question}
`;

console.log(message);

You are a helpful assistant.

Conversation history:
- user: Hello
- assistant: Hi there!

User question:
What is the capital of France?

Dedentation

Strips indentation from multi-line strings.

import { f, If, EndIf } from 'f-strings';

const prompt = f`
      Hello
        World!
          How are you?
      I'm good, thank you!
`;

console.log(dedented);

Hello
  World!
    How are you?
I'm good, thank you!

Lazyness

Expressions can be lazily evaluated, so you can use functions to generate content only when needed.

import { f, If, EndIf } from 'f-strings';

const messages = await getMessages(); 

const prompt = f`
  ${If(messages.length)}
    You have ${messages.length} messages:
    ${() => messages.map((msg) => `- ${msg}`)}
  ${Else}
    No messages.
  ${EndIf}
`;

console.log(prompt);

You have 1000 messages:
- Message 1
- Message 2
...
- Message 1000

API

f - Tagged Template Function

f`template ${value} string`

If(condition) - Conditional Block

Starts a conditional block. Includes the following content if the condition is truthy.

const text = f`
  ${If(condition)}
    content when true
  ${EndIf}
`;

Else() - Alternative Block

Starts an alternative block. Includes the following content if the condition is falsy.

![NOTE] Else can be used without calling it as a function: ${Else} or ${Else()}.

const text = f`
  ${If(condition)}
    content when true
  ${Else}
    content when false
  ${EndIf}
`;

EndIf - End Conditional

Marks the end of a conditional block. Required for every If.

![NOTE] EndIf can be used without calling it as a function: ${EndIf} or ${EndIf()}.

License

MIT