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    1.3.6 • Public • Published


    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>"
    // }


    Use ngx-translate, with yaml files, without runtime loading or parsing. Shows how yaml files can be transformed into json files for ngx-translate to use.


    npm i yaml-import-loader

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