How to npm install on Heroku - json

Question

I would like to to deploy my app on Heroku through bitbucket-pipeline.
Flow is as follows.
composer install
npm install
Laravel-Mix(gulp task and brouserify and so on...)
These will be needed because "vendor" and "node_modules" are written in gitignore.
Now 2 and 3 are failed to build.
I guess it caused package.json or bitbucket-pipelines.yml, but I do not know how to code. Please give me solutions?
※nodejs buildpack is already installed
※I can npm install in Heroku app when I tried "heroku run bash", then "npm install"
Here is my "package.json" and "bitbucket-pipelines.yml" (Laravel5.4)
package.json
{
"private": true,
"scripts": {
"dev": "npm run development",
"development": "cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
"watch": "cross-env NODE_ENV=development node_modules/webpack/bin/webpack.js --watch --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js",
"watch-poll": "npm run watch -- --watch-poll",
"hot": "cross-env NODE_ENV=development node_modules/webpack-dev-server/bin/webpack-dev-server.js --inline --hot --config=node_modules/laravel-mix/setup/webpack.config.js",
"prod": "npm run production",
"production": "cross-env NODE_ENV=production node_modules/webpack/bin/webpack.js --progress --hide-modules --config=node_modules/laravel-mix/setup/webpack.config.js"
},
"devDependencies": {
"axios": "^0.15.3",
"bootstrap-sass": "^3.3.7",
"cross-env": "^3.2.3",
"jquery": "^3.1.1",
"laravel-mix": "0.*",
"lodash": "^4.17.4",
"vue": "^2.1.10"
}
}
bitbucket-pipelines.yml
// bitbucket-pipelines.yml
image: phpunit/phpunit:5.0.3
clone:
depth: full
pipelines:
default:
- step:
script: # Modify the commands below to build your repository.
- composer install
- npm install
- npm run production
- git push https://heroku: test-stg.git HEAD