Uncaught Error: Script error for "popper.js", needed by: bootstrap
https://requirejs.org/docs/errors.html#scripterror
    at makeError (require.js:168)
    at HTMLScriptElement.onScriptError (require.js:1738)

This error is caused by Bootstrap’s dependence on the popper.js component. Bootstrap relies on jQuery or some plug-ins that depend on popper.js.
I found a solution online.

require(["popper"], function(popper) {
    // set popper as required by Bootstrap
    window.Popper = popper;
    require(["bootstrap"], function(bootstrap) {
        // do nothing - just let Bootstrap initialise itself
    });
});

Try it, the problem is still unsolved.
Then start with bootstrap.
The previous code in bootstrap looks like this.

(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ?factory(exports, require('popper.js'), require('jquery')) :
  typeof define === 'function' && define.amd ?define(['exports', 'popper.js', 'jquery'], factory) :
  (factory((global.bootstrap = {}),global.Popper,global.jQuery));
}(this, (function (exports,Popper,$) { 'use strict';

Manually change the configuration in RequireJS to require Paths instead of popper.js. My configuration looks like this.

'popper':                 'popper.js/dist/umd/popper.min',

Therefore, directly change the first few lines of bootstrap source code popper.js to popper to solve the problem.
 
However, I think it is inappropriate to change the source code in this way. So he looked for a solution.
 
The ultimate solution is this.

require.config({
  baseUrl: '/vendors',
  paths: {
    'jquery':                 'jquery/dist/jquery.min',
    'bootstrap':              'bootstrap/dist/js/bootstrap',
    'popper':                 'popper.js/dist/umd/popper.min',
    ...
  },
  shim: {
    'bootstrap': ['jquery']
  },
  map: {
    '*': {
      'popper.js': 'popper'
    }
  }
});

The core solution is:

Add a map configuration in the configuration of require

‘popper.js’: ‘popper’
 
And then I met,
Datatables.net – BS4 relies on datatables.net as well.
Add a row to the map to configure:
‘datatables.net’: ‘datatables’

Reproduced in: https://my.oschina.net/justplay/blog/2992283