Hey there! Let's dig into that Uncaught TypeError: e is not a function error you're hitting with Rollup and Node.js. This usually pops up when you’re expecting a function but getting something else (like undefined, an object, or a primitive value) instead. Let’s break down common culprits across your main.js, _checker.js, and intro.js files:

1. Misaligned Imports/Exports Between Modules #

This is the most frequent cause. Double-check if you’re exporting a non-function value from one file but trying to invoke it as a callback in another:

• For example, if _checker.js has:

  export const validationChecker = "some config string";
  

  But in main.js you write:

  import { validationChecker } from "./_checker.js";
  validationChecker(() => console.log("Done!")); // 💥 Error: validationChecker is a string, not a function
  

• You might also mix up default and named exports. If _checker.js uses export default {} but you import a named function that doesn’t exist, the imported value could be undefined—which will throw this error when you try to call it.

2. Issues with intro.js and Rollup’s Build Pipeline #

Since intro.js is typically injected at the start of your Rollup bundle, it might be accidentally overriding or misinitializing the variable e (or your callback parameter that gets minified to e):

• If intro.js defines a variable e that’s not a function (e.g., const e = "bundle metadata";), this could clash with a callback parameter named e in your code.
• Rollup’s minification or tree-shaking might also be removing your callback function entirely (thinking it’s unused), leaving e as undefined at runtime. Try temporarily disabling minification (remove the terser plugin from your Rollup config) to test this.

3. Incorrect Callback Parameter Passing #

You might be passing a non-function value where a callback is expected:

• For example, in main.js you do:

  import { runCheck } from "./_checker.js";
  runCheck({ timeout: 5000 }); // Passing an object instead of a function
  

  But _checker.js expects a callback:

  export function runCheck(callback) {
    callback(); // 💥 Error if callback isn't a function
  }
  

• Async operations (like Promises) are another common spot—if you pass a non-function to .then() or .catch(), you’ll hit this exact error.

4. Variable Scoping Conflicts #

If e is a callback parameter in your code, it might be getting overwritten by a higher-scoped variable with the same name:

const e = "global value";
someAsyncTask(e => {
  e(); // 💥 Here, `e` is supposed to be the callback parameter, but if the outer `e` is accidentally referenced instead (unlikely, but possible with messy scoping), it’ll fail
});

Quick Debugging Tips #

• Add type checks: Before invoking a callback, verify it’s actually a function. For example in _checker.js:

  export function runCheck(callback) {
    console.log("Callback type:", typeof callback); // Check if this logs 'function'
    if (typeof callback === "function") {
      callback();
    } else {
      console.error("Invalid callback received:", callback);
    }
  }
  

• Inspect the bundled output: Look at Rollup’s final build file to see what e corresponds to—this will reveal if it’s been minified incorrectly or replaced with an unexpected value.
• Validate exports: Double-check every export in _checker.js and import in main.js to ensure you’re pulling in the right function.

内容的提问来源于stack exchange，提问作者PatricNox