How to fix the error; 'Error: Bootstrap tooltips require Tether (http://github.hubspot.com/tether/)'

Question

For Bootstrap 4 stable:

Since beta Bootstrap 4 doesn't depend on Tether but Popper.js. All scripts (must be in this order):

<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>

See the current documentation for the newest script versions.

---

Only Bootstrap 4 alpha:

Bootstrap 4 alpha needs Tether, so you need to include tether.min.js before you include bootstrap.min.js, eg.

<script src="https://npmcdn.com/[email protected]/dist/js/tether.min.js"></script>
<script src="https://npmcdn.com/[email protected]/dist/js/bootstrap.min.js"></script>

If you're using Webpack:

1. Set up bootstrap-loader as described in docs;
2. Install tether.js via npm;
3. Add tether.js to the webpack ProvidePlugin plugin.

webpack.config.js:

plugins: [
        <... your plugins here>,
        new webpack.ProvidePlugin({
            $: "jquery",
            jQuery: "jquery",
            "window.jQuery": "jquery",
            "window.Tether": 'tether'
        })
    ]

Source

If you are using npm and browserify:

// es6 imports
import tether from 'tether';
global.Tether = tether;

// require
global.Tether = require('tether');

Personally I use small subset of Bootstrap functionality and don't need to attach Tether.

This should help:

window.Tether = function () {
  throw new Error('Your Bootstrap may actually need Tether.');
};

If you want to avoid the error message and you are not using Bootstrap tool tips, you can define window.Tether before loading Bootstrap.

<script>
  window.Tether = {};
</script>
<script src="js/bootstrap.min.js"></script>

You should done my guideline:
1. Add bellow source into Gemfile

source 'https://rails-assets.org' do
  gem 'rails-assets-tether', '>= 1.1.0'
end

2. Run command:

   bundle install

3. Add this line after jQuery in application.js.

   //= require jquery
   //= require tether

4. Restart rails server.

Install tether via npm like below

npm install tether --save-dev

then add tether to your html above bootstrap like below

<script src="node_modules/tether/dist/js/tether.min.js"></script>
<script src="jspm_packages/github/twbs/[email protected]/js/bootstrap.js"></script>