Install npm and bower packages using composer - Drupal

Add repositories to composer.json

"repositories": [
    {
      "type": "composer",
      "url": "https://packages.drupal.org/8"
    },
    {
       "type": "composer",
       "url": "https://asset-packagist.org"
     }
],

Add bower-asset & npm-asset to installer-types

"installer-types": [
    "bower-asset",
    "npm-asset",
    "drupal-drush",
    "drupal-theme",
    "drupal-profile",
    "drupal-module",
    "drupal-core"
],

Update installer-paths for libraries

"installer-paths": {
    "web/core": ["type:drupal-core"],
    "web/libraries/{$name}": [
        "type:drupal-library",
        "type:bower-asset",
        "type:npm-asset"
    ],
    "web/modules/contrib/{$name}": ["type:drupal-module"],
    "web/profiles/contrib/{$name}": ["type:drupal-profile"],
    "web/themes/contrib/{$name}": ["type:drupal-theme"],
    "drush/Commands/contrib/{$name}": ["type:drupal-drush"],
    "web/modules/custom/{$name}": ["type:drupal-custom-module"],
    "web/profiles/custom/{$name}": ["type:drupal-custom-profile"],
    "web/themes/custom/{$name}": ["type:drupal-custom-theme"],
    "web/private/scripts/quicksilver/{$name}/": ["type:quicksilver-script"]
},

Now we will be able to install npm and bower packages using composer and those packages will download into web/libraries. Run the following composer command to try it.

composer require npm-asset/bootstrap