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ember-template-recast

With ember-template-recast, transform a template's AST and reprint it. Its formatting will be preserved.

For instance, it is possible to change a component's property while preserving its formatting:

const recast = require('ember-template-recast');

const template = `
<Sidebar
  foo="bar"
     item={{hmmm}}
/>
`;

// parse
let ast = recast.parse(template);

// transform
ast.body[1].attributes[1].value.path = builders.path('this.hmmm');

// print
let ouput = recast.print(ast);

output === `
<Sidebar
  foo="bar"
     item={{this.hmmm}}
/>
`; // is true!

Command Line Usage

ember-template-recast comes with a binary for running a transform across multiple files, similar to jscodeshift.

npx ember-template-recast directory/of/templates -t transform.js

Example transform plugin:

module.exports = (env) => {
  let { builders: b } = env.syntax;

  return {
    MustacheStatement() {
      return b.mustache(b.path('wat-wat'));
    },
  };
};

APIs

parse

Used to parse a given template string into an AST. Generally speaking, this AST can be mutated and passed into print (docs below).

const templateRecast = require('ember-template-recast');
const template = `
{{foo-bar
  baz="stuff"
}}
`;
let ast = templateRecast.parse(template);
// now you can work with `ast`

print

Used to generate a new template string representing the provided AST.

const templateRecast = require('ember-template-recast');
const template = `
{{foo-bar
  baz="stuff"
}}
`;
let ast = templateRecast.parse(template);
ast.body[0].hash[0].key = 'derp';

templateRecast.print(ast);

    {{foo-bar
      derp="stuff"
    }}

transform

Used to easily traverse (and possibly mutate) a given template. Returns the resulting AST and the printed template.

The plugin argument has roughly the following interface:

export interface Syntax {
  parse: typeof preprocess;
  builders: typeof builders;
  print: typeof print;
  traverse: typeof traverse;
  Walker: typeof Walker;
}

export interface TransformPluginEnv {
  syntax: Syntax;
  contents: string;
  filePath?: string;
  parseOptions: {
    srcName?: string;
  };
}

export interface TransformPluginBuilder {
  (env: TransformPluginEnv): NodeVisitor;
}

The list of known builders on the env.syntax.builders are found here, although there are a few small extensions related to formatting in custom-nodes.ts

Example:

const { transform } = require('ember-template-recast');

const template = `
{{foo-bar
  baz="stuff"
}}
`;

let { code } = transform({
  template,
  plugin(env) {
    let { builders: b } = env.syntax;

    return {
      MustacheStatement() {
        return b.mustache(b.path('wat-wat'));
      },
    };
  }
});

console.log(code); // => {{wat-wat}}

SemVer Policy

Due to usage of TypeScript and bundling external APIs this project has somewhat unique SemVer commitments. A high level summary is:

Major Version

The following are scenarios that would cause a major version (aka breaking change) release:

  • Dropping support for Node versions (e.g. dropping Node 12 support)
  • Non-additive changes to the underlying AST (which we bundle from @glimmer/syntax)
  • Breaking changes to the @glimmer/syntax builder APIs

Minor Version

The following are scenarios that would cause a minor version (aka new feature) release:

  • Changes to TypeScript version used internally by ember-template-recast
  • Changes to make the types used by ember-template-recast to be more accurate (e.g. narrowing / broadening of previously published types).
  • Adding new features

Patch Version

The following are scenarios that would cause a patch release:

  • Bug fixes to internal re-writing logic
  • Bug fix releases of @glimmer/syntax

License

This project is distributed under the MIT license, see LICENSE for details.