Converting Handlebars AST to Template Strings with hbs-ast-to-str
Tags: handlebars, javascript, opensource, typescript
Published: 2023-10-23 04:47:00


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[`Handlebars.js`](https://handlebarsjs.com/) is a popular templating engine that allows you to create dynamic templates for your web applications. When you use Handlebars, you often work with Abstract Syntax Trees (ASTs) to manipulate and process templates. But have you ever needed to convert an AST back into a template string? That's where the "hbs-ast-to-str" package comes in.

## Introduction to `hbs-ast-to-str`

The [hbs-ast-to-str](https://www.npmjs.com/package/hbs-ast-to-str) package is a NodeJS library that lets you convert Handlebars ASTs back into template strings with optional modifications. It's a handy tool for those times when you need to reverse the process and generate a template string from an AST.

### Installation

You can install `hbs-ast-to-str` via `npm` as well as `yarn`:

```bash
npm install hbs-ast-to-str
```

```bash
yarn add hbs-ast-to-str
```

## Basic Usage

Let's take a look at how you can use `hbs-ast-to-str` in your projects.

### Without Modifications

If you just want to convert an AST to a template string without any modifications, here's how you can do it:

```javascript
const { convertAstToString } = require('hbs-ast-to-str');

const ast = /* Your Handlebars AST using Handlebars.parse(template_str) */;

const template = convertAstToString(ast);
```

### With Modifications

In some cases, you may want to make specific modifications during the conversion process. You can achieve this with the "ModificationOptions" interface. Here's an example:

```javascript
const { convertAstToString } = require('hbs-ast-to-str');

const ast = /* Your Handlebars AST using Handlebars.parse(template_str) */;

const options = {
  helper: 'filter',
  paramType: HbsNodeTypes.SubExpression,
  paramPosition: 2,
  modifiers: [(d) => `'${d}'`],
};

const template = convertAstToString(ast, options);
```

## The ModificationOptions Interface

The heart of this package is the "ModificationOptions" interface, which defines a set of options for making modifications to specific nodes or elements in a Handlebars template. Let's delve into the properties of this interface:

- `helper`: An optional string that specifies the name of the helper function. This can be used to associate a modification with a particular helper.

- `paramType`: An enumeration that represents the type of parameter you want to modify. You can use `HbsNodeType` to specify the node type.

- `paramPosition`: An integer that specifies the position of the parameter you want to modify. This is particularly useful when dealing with helper parameters.

- `modifiers`: An array of functions that define the modifications to be applied. Each function in the array should implement the logic for the modification.

Here's an example of how you can use the "ModificationOptions" interface in TypeScript:

```javascript
const options = {
  helper: 'customHelper',
  paramType: HbsNodeType.Block,
  paramPosition: 2,
  modifiers: [(parameterValue) => {
    // Implement your modification logic here.
    // Modify the 'parameterValue' as needed.
  }],
};
```

## Conclusion

The `hbs-ast-to-str` package is a powerful tool for developers working with Handlebars templates. Whether you need to convert an AST back into a template string or make specific modifications during the process, this package has you covered. It simplifies the task of working with Handlebars ASTs and empowers you to create dynamic and flexible templates for your web applications.

To learn more and explore the details, refer to the spec file included with the package.

> So, if you find yourself dealing with Handlebars ASTs in your projects, give `hbs-ast-to-str` a try and streamline your templating workflow.