A customizable YAML loader for Webpack supporting the '!import <file>' type to include different YAML files, and '!import-raw <file>' type to include the string contents of any file.

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A customizable YAML loader for Webpack supporting the !import <file> type to include different YAML files, and !import-raw <file> type to include the string contents of any file.
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npm install --save-dev yaml-import-loader


Input files

### ./main.yml
local:  !import ./hello_world.yml
module: !import module/array.yml
url:    !import https://fake.url/old.json
raw:    !import-raw ./plain.html

### ./hello_world.yml
hello: world

### module/array.yml
- elem1
- elem2

### https://fake.url/old.json
  "jsonKey": "jsonValue"

<!-- plain.html -->
<p>Some paragraph...</p>

JSON output

    "local": {
        "hello": "world"
    "module": ["elem1", "elem2"],
    "url": {
        "jsonKey": "jsonValue"
    "raw": "<!-- plain.html -->\n<div>Hey!</div>\n<p>Some paragraph...</p>"


This loader is supposed to be used with Webpack. The configuration snippet below is not a complete webpack configuration and only demonstrates how to configure this loader. Check the documentation for information on how to configure webpack. The parser options are passed to the YAML parser: js-yaml. You can find more information about those options on their README.

Webpack - module.rules entry

  test: /\.ya?ml$/,
  use: {
    loader: 'yaml-import-loader'

    // Note: The options below are the default options
    options: {

      // Allows the use of the `!import <file>` type without assigning it to a
      // key. Using this will cause the target's file content to be inserted at
      // the import location.
      importRoot: false,

      // Allows the use of the `!import <file>` type with assigned to a key.
      // Settings this and the `importRoot` options to false will result in a
      // regular yaml-loader.
      importNested: true,

      // The import keyword used for yaml/json content.
      importKeyword: 'import',

      // The import-raw keyword used for raw file content.
      importRawKeyword: 'import-raw',

      // The output type. Can be 'object', 'json', or 'yaml'
      // 'object' -> exported js object
      // 'json'   -> stringified json
      // 'yaml'   -> stringified yaml
      output: 'object',

      // The parser options are passed to js-yaml.
      parser: {

        // Custom types to be used by the parser, details below.
        types: [],

        // The base schema to extend, can be an array of schemas.
        schema: require('js-yaml').SAFE_SCHEMA,

        // Allows duplicate keys to be used. The old value of a duplicate key
        // will be overwritten by the new value (`json` option in `js-yaml`).
        allowDuplicate: true,

        // The function to call on warning messages. By default the parser will
        // throw on warnings.
        onWarning: undefined

Root imports

If you set the importRoot option to true, the yaml-import-loader will allow you to import multiple files at the root level. This will insert the file contents at the import location.
!import ./root-import1.yml
!import ./root-import2.yml

nested: !import ./nested-import.yml

You must ensure that you do not mix types at the root level. If the file contains a mapping at the root level all root imports must import a mapping, if the root level contains array elements every root import must import array elements. If this is not the case parsing will fail.

Custom types

This loader internally uses js-yaml for parsing, check their wiki for examples on using custom types. The types option accepts an array with Type objects, and functions returning a Type object. If you create your type in a function you will get context in the first parameter, with this context you can instruct the loader to resolve promises.
const { Type } = require('js-yaml');

let types = [
  ctx => new Type('!async', {
    kind: 'mapping',
    resolve: data => {
        data !== null &&
        typeof data.delay === 'number' &&
        typeof data.result === 'string';
    construct: data => {
      ctx.resolveAsync = true;
      return new Promise(resolve => {
        setTimeout(() => resolve(data.result), data.delay);
    instanceOf: String

When passing the types array above to the loader we are allowed to use the !async type in our imported yaml files. Note that the delay here is for demonstration purposes, you can return the result directly instead of returning a Promise.
# YAML input
result: !async
  delay: 1000
  result: 'I will be resolved after 1 second, asynchronously!'

# JSON output
  "result": "I will be resolved after 1 second, asynchronously!"

Use cases

Basic usage

const yaml = require('./main.yml');

// world

console.log(JSON.stringify(yaml, undefined, 4));
// {
//   "local": {
//    "hello": "world"
//   },
//   "module": [
//     "elem1",
//     "elem2"
//   ],
//   "url": {
//     "jsonKey": "jsonValue"
//   },
//   "raw": "<!-- plain.html -->\n<div>Hey!</div>\n<p>Some paragraph...</p>"
// }


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