npm 6 · npm
The message
npm WARN react-dom@17.0.2 requires a peer of react@17.0.2 but none is installed.
What it means
npm 6 only warned about peer dependencies and never installed them for you: the package is present, but the companion it says it needs is not. It appears in a project still on npm 6, or when you are using an old lockfile made in that era. Install the named peer yourself at a version inside the printed range and it is done. Nothing has failed yet because this is only a warning, but it comes back later as Cannot find module, or as two copies of the same library producing errors that make no sense.
The fix
There is no one-line command for this. The explanation says what to look at instead.
- Printed by
- npm 6
- npm
- 20
With npm the cause sits in the first code XXXX line rather than the last six npm ERR! lines, and when the failure comes from the dependency tree or a native build instead of your own code, deleting node_modules and installing again clears about half of them.
Reading an error message
- Read from the first line down. The lower you go the more it is about the tool’s internals; the cause is usually at the top.
- If there is a file and a line number, start there — not the top stack frame, but the topmost line that names a file you wrote.
- Search the message verbatim, but strip your own paths and variable names first; those are what stop the search from matching.
- The same condition is worded differently across tool versions. If results look wrong, add the version number to the query.
- Before pasting a fix, check what it throws away. Some of these cannot be undone.
Common questions
Q. What does “npm WARN react-dom@17.0.2 requires a peer of react@17.0.2 but none is installed.” mean?
npm 6 only warned about peer dependencies and never installed them for you: the package is present, but the companion it says it needs is not. It appears in a project still on npm 6, or when you are using an old lockfile made in that era. Install the named peer yourself at a version inside the printed range and it is done. Nothing has failed yet because this is only a warning, but it comes back later as Cannot find module, or as two copies of the same library producing errors that make no sense.
Q. How do I fix it?
There is no one-line command. The explanation above says what to look at instead.
Q. Which tool prints this?
npm 6. It sits under npm, and the message runs to 12 words.