RequireJS environment in browser will break the UMD module conversion

Describe the bug

Say I have an umd module

;(function(root, factory) {
    // istanbul ignore next
    if (typeof define === "function" && define.amd) {
        // istanbul ignore next
        define([], factory)
    } else if (typeof module === "object" && module.exports) {
        module.exports = factory()
    } else {
        // istanbul ignore next
        root.regexpToAst = factory()
    }
})(
    typeof self !== "undefined"
        ? // istanbul ignore next
          self
        : this,
    function() {}
)

With the commonjs conversion, it returns code like

var require_regexp_to_ast = __commonJS({
  "../../node_modules/regexp-to-ast/lib/regexp-to-ast.js"(exports, module) {
    (function(root, factory) {
      if (typeof define === "function" && define.amd) {
        define([], factory);
      } else if (typeof module === "object" && module.exports) {
        module.exports = factory();
      } else {
        root.regexpToAst = factory();
      }
    })(typeof self !== "undefined" ? self : exports, function() {
      function RegExpParser2() {
      }

But this will break in runtime because there is global define in the browser since I have a requireJS environment. This module will be registered in the global AMD module instead of vite ESM module.

Validations

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• Read the Contributing Guidelines.
• Read the docs.
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• Make sure this is a Vite issue and not a framework-specific issue. For example, if it’s a Vue SFC related bug, it should likely be reported to https://github.com/vuejs/vue-next instead.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[pakholeung37]

Published a plugin to handle this case vite-plugin-treat-umd-as-commonjs.

[jkone27]

this would be very useful for migrating legacy projects like apps using durandaljs and so… or other apps using requirejs amd modules