typesafe-templates

Template engine for writing compiler-checked templates in TypeScript by leveraging JSX to generate JavaScript code from TypeScript code files rather than text templates.

Under the hood, typesafe-templates uses Babel to build an AST, which is then traversed to find and replace JSX nodes. Such a tool can be useful for pre-generating customized Javascript files that vary by user or for creating HTML templates using JSX rather than a syntax like Pug (some limitations apply).

Example

template.tsx

interface Message {
    name: string;
    lang: 'en' | 'es';
}

(function() {
    <$repeat items={$.messages}>
        {($: Message) => {
            <$if test={$.lang === 'en'}>
                console.log('Good morning' + <$string value={$.name} />);
            </$if>;
        	<$if test={$.lang === 'es'}>
                console.log('Bueños dias' + <$string value={$.name} />);
            </$if>;
        }}
    </$repeat>
})();

script.ts

import { renderFile } from 'typesafe-templates';

async function main() {
    const data: { messages: Message[] } = {
        messages: [
            { name: 'Alice', lang: 'en' },
            { name: 'Bob', lang: 'en' },
            { name: 'Dora', lang: 'es' },
            { name: 'Diego', lang: 'es' }
        ]
    };
    
    const { code } = await renderFile('./template.tsx', data);
    console.log(code);
}

main();

Output

(function() {
    console.log('Good morning, Alice');
    console.log('Good morning, Bob');
    console.log('Bueños dias, Dora');
    console.log('Bueños dias, Diego');
})();

Installation

npm install typesafe-templates

Use the --save-dev flag if you will be generating templates as part of a development task.

Usage

To work properly you will need to include a type definition for JSX elements that assigns JSX.Element to any.

declare namespace JSX {
    type Element = any;
}

As a convenience, the $ symbol is used to represent a parent type of a scope. However, any name can be used. Presently the library does not support deep properties. A reference like $.level1.level2.level3 may type-check correctly, but the proper value will not be injected into the template.

Elements

Control Elements

Control elements are similar to JavaScript control blocks. They wrap a block of code and control its output into the rendered code. In JSX terms, they require props.children to be defined.

Because JSX is used here as substitute JavaScript expressions, you will often need to include a semicolon after the tag as you would with a normal statement.

<$if test={} />

Controls whether the wrapped contents will appear in the output.

<$repeat items={} />

Repeats the wrapped contents for each item in items. For each copy, a new data scope is created and set to value of the current item.

The $repeat element expects the children prop to be a function or arrow function expression; however, this surrounding function will be removed in the final output.

Example:

<$repeat items={$.messages}>
    {($: Message) => {
    	console.log(<$string value={$.name}>)
    }}
</$repeat>

Injection Elements

<$boolean value={} />

Outputs a boolean literal.

<$expr code={} />

Takes in a string representing an expression, parses it into AST, and adds the resultant node into the output.

<$number value={} />

Outputs a numeric literal.

<$string value={} />

Outputs a string literal.

Limitations

Currently TypeScript treats all JSX elements as the same type (which can be changed but only to one collective type). Therefore elements, when used as values, are treated as any and will not show type errors unless you manually typecast the element. Refactoring signatures, however, will work when using TS tooling to rearrange arguments.

Example:

function print(str: string, num: number, bool: boolean) {}

print(<$string />, <$string />, <$string />); // Will not report type errors

print(<$string /> as string, <$string /> as string, <$string /> as string); // Will report type errors