ERROR Cannot read properties of undefined (reading 'length')

[sgielen]

I get this error when trying to run npm-why in my project.

The initial reason for this error is in npm-why's main, which hides the actual error:

async function main (dir, packageName) {
  const reasons = await collectReasons(dir, packageName).catch(e => {
    if (e.code === 'ENOLOCK') {
      throw new Error('package.json or lockfile not found.')
    }
  })

  if (!reasons.length) { // <-- error is thrown here

The actual error can be shown by changing this to:

async function main (dir, packageName) {
  const reasons = await collectReasons(dir, packageName).catch(e => {
    if (e.code === 'ENOLOCK') {
      throw new Error('package.json or lockfile not found.')
    } else {
      throw e;
    }
  })

  if (!reasons.length) {

I suggest to make this change upstream, because then npm-why shows the actual error:

  ERROR Maximum call stack size exceeded

See also #220.

This seems to be because of a recursive dependency, I'm investigating further.

[sgielen]

It's because of a circular dependency that's easily reproduced in an empty directory:

npm install --save-dev eslint
npm-why eslint

There is an edge from eslint to eslint-utils, and from eslint-utils back to eslint, and this circular dependency eventually causes npm-why to encounter a "maximum call stack size exceeded".

[sgielen]

In buildDependentsTree we can detect this circular dependency and prevent further recursion, while still reporting the circular dependency. Here's some example code that does this, but I'm sure there's a prettier solution:

function buildDependentsTree (node, paths = [], leafs = [], depth = true) {
  const { name, version, edgesIn } = node

  // when leaf node
  if (edgesIn.size === 0) {
    leafs.push(paths)
    return { name, version, leafs }
  }

  // prevent dead loops
  if (paths.includes(name)) {
    return { name, version, leafs }
  }

  let dependents = []
  if (depth) {
    dependents = Array.from(edgesIn).map(edge => {
      const pkg = { name, version }
      return buildDependentsTree(edge.from, paths.concat(pkg), leafs, !paths.map(p => p.name).includes(name))
    })
  }

  return { name, version, leafs, dependents }
}

With this, the output of the reproduction above becomes the following, which clearly shows the recursion:

$  npm-why eslint

  Who required eslint:

  2021-11-08-11-05-29 > eslint@8.2.0
  2021-11-08-11-05-29 > eslint > eslint-utils > eslint@8.2.0

[sgielen]

Actually, I see now that the "prevent dead loops" check was intended to fix this, but it doesn't work, since paths contains {name, version} structs and not just name strings. So this also fixes the issue:

   // prevent dead loops
-  if (paths.includes(name)) {
+  if (paths.map(p => p.name).includes(name)) {
     return { name, version, leafs }
   }

However, it does not show the recursion in the output:

$ npm-why eslint

  Who required eslint:

  2021-11-08-11-36-29 > eslint@8.2.0

[sgielen]

@amio any updates perhaps to the two improvements suggested in this issue?

[sgielen]

@amio I've added #349, which includes a fix for this issue, a test for that, a fix for the issue hiding the actual exception.

[sgielen]

Fixed by #349!