With Node.js v12.11.1, On Windows 10,

node --experimental-modules test.js

console.log("version:", process.version)

;(async () => {
    console.log("==== ESM ====")
    await import("x-esm") //→ Found as expected
    await import("./node_modules/x-esm/index.js?q=0") //→ Found and `x-esm` re-ran as expected
    await import("./node_modules/x-esm/index.js?q=1") //→ Found and `x-esm` re-ran as expected

    console.log("==== CJS ====")
    const cjs = await import("x-cjs") //→ Found as expected
    const cjs0 = await import("./node_modules/x-cjs/index.js?q=0") //→ Found but `x-cjs` didn't re-run
    const cjs1 = await import("./node_modules/x-cjs/index.js?q=1") //→ Found but `x-cjs` didn't re-run
    console.log(cjs === cjs0, cjs === cjs1, cjs0 === cjs1) //→ all are false but `x-cjs` didn't run three times
    
    console.log("---- remove 'require.cache' ----")
    delete require.cache[require.resolve("x-cjs")]
    await import("x-cjs") //→ Found but `x-cjs` didn't re-run
    await import("./node_modules/x-cjs/index.js?q=0") //→ Found but `x-cjs` didn't re-run
    await import("./node_modules/x-cjs/index.js?q=1") //→ Found but `x-cjs` didn't re-run
    await import("./node_modules/x-cjs/index.js?q=2") //→ Found and `x-cjs` re-ran as expected
    await import("./node_modules/x-cjs/index.js?q=3") //→ Found but `x-cjs` didn't re-run
})().catch(error => {
    console.error(error)
    process.exitCode = 1
})

(node:14972) ExperimentalWarning: The ESM module loader is experimental.
version: v12.11.1
==== ESM ====
x-esm
x-esm
x-esm
==== CJS ====
x-cjs
false false false
---- remove 'require.cache' ----
x-cjs

I tried to import packages without import cache. From the document, it looks I should use query strings.

    await import("x-esm") //→ Found as expected
    await import("./node_modules/x-esm/index.js?q=0") //→ Found and `x-esm` re-ran as expected
    await import("./node_modules/x-esm/index.js?q=1") //→ Found and `x-esm` re-ran as expected

x-esm is an ES module package. It worked as expected.

    const cjs = await import("x-cjs") //→ Found as expected
    const cjs0 = await import("./node_modules/x-cjs/index.js?q=0") //→ Found but `x-cjs` didn't re-run
    const cjs1 = await import("./node_modules/x-cjs/index.js?q=1") //→ Found but `x-cjs` didn't re-run
    console.log(cjs === cjs0, cjs === cjs1, cjs0 === cjs1) //→ all are false but `x-cjs` didn't run three times

x-cjs is a CJS package. The result was odd. The console.log() in x-cjs package ran only one time, but the returned values are different for each query string.

I found the entry of x-cjs in require.cache. However, the cache entry is odd as well. It's different from require("x-cjs"), the entry doesn't have parent property and the module.children of test.js is still empty.

Anyway, I tried to remove the cache entry.

    console.log("---- remove 'require.cache' ----")
    delete require.cache[require.resolve("x-cjs")]
    await import("x-cjs") //→ Found but `x-cjs` didn't re-run
    await import("./node_modules/x-cjs/index.js?q=0") //→ Found but `x-cjs` didn't re-run
    await import("./node_modules/x-cjs/index.js?q=1") //→ Found but `x-cjs` didn't re-run
    await import("./node_modules/x-cjs/index.js?q=2") //→ Found and `x-cjs` re-ran as expected
    await import("./node_modules/x-cjs/index.js?q=3") //→ Found but `x-cjs` didn't re-run

Cryptic. I guess this behavior is:

• import(cjs) has cache apart from require.cache.
• The import(cjs) cache is created from require.cache.
• It runs CJS package only if require.cache entry was not found.
• The import(cjs) cache is not removed even if require.cache entry deleted.

Therefore, I have to do the following steps if I want to import packages without cache.

1. Find the main file of the package because I cannot put query strings to the package name.

   const url = "file:" + require.resolve(packageName) + uniqueQueryString;

2. Import it.

   const ret = await import(url);

3. Delete require.cache entry.

   delete require.cache[require.resolve(packageName)];

1. Is it intentional behavior that import(cjs) creates incomplete require.cache entries?
2. If yes, is it intentional behavior that import(cjs) with query strings returns different objects for the same CJS package?

I'm guessing that import(cjs) should not create any require.cache entries, and import(cjs) with query strings re-runs CJS packages as same as ES packages.