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有个项目在 mac 下开发，安装包 npm i，一切正常；
把这个项目放到 linux 机器上，安装包 npm i，报了一堆 warning：
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: fsevents@^1.2.7 (node_modules/chokidar/node_modules/fsevents):
npm WARN notsup SKIPPING OPTIONAL DEPENDENCY: Unsupported platform for fsevents@1.2.7: wanted {“os”:”darwin”,”arch”:”any”} (current: {“os”:”linux”,”arch”:”x64″})
npm WARN 0403@1.0.0 No description
npm WARN 0403@1.0.0 No repository field.
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: abbrev@1.1.1 (node_modules/fsevents/node_modules/abbrev):
npm WARN enoent SKIPPING OPTIONAL DEPENDENCY: ENOENT: no such file or directory, rename ‘/root/2019/0403/node_modules/fsevents/node_modules/abbrev’ -> ‘/root/2019/0403/node_modules/fsevents/node_modules/.abbrev.DELETE’
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: ansi-regex@2.1.1 (node_modules/fsevents/node_modules/ansi-regex):
npm WARN enoent SKIPPING OPTIONAL DEPENDENCY: ENOENT: no such file or directory, rename ‘/root/2019/0403/node_modules/fsevents/node_modules/ansi-regex’ -> ‘/root/2019/0403/node_modules/fsevents/node_modules/.ansi-regex.DELETE’
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: aproba@1.2.0 (node_modules/fsevents/node_modules/aproba):
npm WARN enoent SKIPPING OPTIONAL DEPENDENCY: ENOENT: no such file or directory, rename ‘/root/2019/0403/node_modules/fsevents/node_modules/aproba’ -> ‘/root/2019/0403/node_modules/fsevents/node_modules/.aproba.DELETE’
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: balanced-match@1.0.0 (node_modules/fsevents/node_modules/balanced-match):
npm WARN enoent SKIPPING OPTIONAL DEPENDENCY: ENOENT: no such file or directory, rename ‘/root/2019/0403/node_modules/fsevents/node_modules/balanced-match’ -> ‘/root/2019/0403/node_modules/fsevents/node_modules/.balanced-match.DELETE’
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: chownr@1.1.1 (node_modules/fsevents/node_modules/chownr):
npm WARN enoent SKIPPING OPTIONAL DEPENDENCY: ENOENT: no such file or directory, rename ‘/root/2019/0403/node_modules/fsevents/node_modules/chownr’ -> ‘/root/2019/0403/node_modules/fsevents/node_modules/.chownr.DELETE’
npm WARN optional SKIPPING OPTIONAL DEPENDENCY: code-point-at@1.1.0 (node_modules/fsevents/node_modules/code-point-at):
npm WARN enoent SKIPPING OPTIONAL DEPENDENCY: ENOENT: no such file or directory, rename ‘/root/2019/0403/node_modules/fsevents/node_modules/code-point-at’ -> ‘/root/2019/0403/node_modules/fsevents/node_modules/.code-point-at.DELETE’
…
执行 npm ls，有不少 UNMET OPTIONAL DEPENDENCY 的模块，最后还报了一堆错：
│ ├── define-property@2.0.2 deduped
│ ├── extend-shallow@3.0.2 deduped
│ ├── regex-not@1.0.2 deduped
│ └─┬ safe-regex@1.1.0
│ └── ret@0.1.15
├─┬ UNMET OPTIONAL DEPENDENCY fsevents@1.2.7
│ ├── nan@2.13.2
│ └─┬ UNMET OPTIONAL DEPENDENCY node-pre-gyp@0.10.3
│ ├── UNMET OPTIONAL DEPENDENCY detect-libc@1.0.3
│ ├─┬ UNMET DEPENDENCY mkdirp@0.5.1
│ │ └── UNMET DEPENDENCY minimist@0.0.8
│ ├─┬ UNMET OPTIONAL DEPENDENCY needle@2.2.4
│ │ ├─┬ UNMET OPTIONAL DEPENDENCY debug@2.6.9
│ │ │ └── UNMET OPTIONAL DEPENDENCY ms@2.0.0
│ │ ├─┬ UNMET OPTIONAL DEPENDENCY iconv-lite@0.4.24
│ │ │ └── UNMET OPTIONAL DEPENDENCY safer-buffer@2.1.2
│ │ └── UNMET OPTIONAL DEPENDENCY sax@1.2.4
│ ├─┬ UNMET OPTIONAL DEPENDENCY nopt@4.0.1
│ │ ├── UNMET OPTIONAL DEPENDENCY abbrev@1.1.1
│ │ └─┬ UNMET OPTIONAL DEPENDENCY osenv@0.1.5
│ │ ├── UNMET OPTIONAL DEPENDENCY os-homedir@1.0.2
│ │ └── UNMET OPTIONAL DEPENDENCY os-tmpdir@1.0.2
│ ├─┬ UNMET OPTIONAL DEPENDENCY npm-packlist@1.2.0
│ │ ├─┬ UNMET OPTIONAL DEPENDENCY ignore-walk@3.0.1
│ │ │ └─┬ UNMET DEPENDENCY minimatch@3.0.4
│ │ │ └─┬ UNMET DEPENDENCY brace-expansion@1.1.11
│ │ │ ├── UNMET DEPENDENCY balanced-match@1.0.0
│ │ │ └── UNMET DEPENDENCY concat-map@0.0.1
│ │ └── UNMET OPTIONAL DEPENDENCY npm-bundled@1.0.5
│ ├─┬ UNMET OPTIONAL DEPENDENCY npmlog@4.1.2
│ │ ├─┬ UNMET OPTIONAL DEPENDENCY are-we-there-yet@1.1.5
│ │ │ ├── UNMET OPTIONAL DEPENDENCY delegates@1.0.0
│ │ │ └─┬ UNMET OPTIONAL DEPENDENCY readable-stream@2.3.6
│ │ │ ├── UNMET OPTIONAL DEPENDENCY core-util-is@1.0.2
│ │ │ ├── UNMET DEPENDENCY inherits@2.0.3
│ │ │ ├── UNMET OPTIONAL DEPENDENCY isarray@1.0.0
│ │ │ ├── UNMET OPTIONAL DEPENDENCY process-nextick-args@2.0.0
│ │ │ ├── UNMET DEPENDENCY safe-buffer@5.1.2
│ │ │ ├─┬ UNMET OPTIONAL DEPENDENCY string_decoder@1.1.1
│ │ │ │ └── UNMET DEPENDENCY safe-buffer@5.1.2
│ │ │ └── UNMET OPTIONAL DEPENDENCY util-deprecate@1.0.2
│ │ ├── UNMET DEPENDENCY console-control-strings@1.1.0
│ │ ├─┬ UNMET OPTIONAL DEPENDENCY gauge@2.7.4
│ │ │ ├── UNMET OPTIONAL DEPENDENCY aproba@1.2.0
│ │ │ ├── UNMET DEPENDENCY console-control-strings@1.1.0
│ │ │ ├── UNMET OPTIONAL DEPENDENCY has-unicode@2.0.1
│ │ │ ├── UNMET OPTIONAL DEPENDENCY object-assign@4.1.1
│ │ │ ├── UNMET OPTIONAL DEPENDENCY signal-exit@3.0.2
│ │ │ ├─┬ UNMET DEPENDENCY string-width@1.0.2
│ │ │ │ ├── UNMET DEPENDENCY code-point-at@1.1.0
│ │ │ │ ├─┬ UNMET DEPENDENCY is-fullwidth-code-point@1.0.0
│ │ │ │ │ └── UNMET DEPENDENCY number-is-nan@1.0.1
│ │ │ │ └── UNMET DEPENDENCY strip-ansi@3.0.1
│ │ │ ├─┬ UNMET DEPENDENCY strip-ansi@3.0.1
│ │ │ │ └── UNMET DEPENDENCY ansi-regex@2.1.1
│ │ │ └─┬ UNMET OPTIONAL DEPENDENCY wide-align@1.1.3
│ │ │ └── UNMET DEPENDENCY string-width@1.0.2
│ │ └── UNMET OPTIONAL DEPENDENCY set-blocking@2.0.0
│ ├─┬ UNMET OPTIONAL DEPENDENCY rc@1.2.8
│ │ ├── UNMET OPTIONAL DEPENDENCY deep-extend@0.6.0
│ │ ├── UNMET OPTIONAL DEPENDENCY ini@1.3.5
│ │ ├── UNMET OPTIONAL DEPENDENCY minimist@1.2.0
│ │ └── UNMET OPTIONAL DEPENDENCY strip-json-comments@2.0.1
│ ├─┬ UNMET OPTIONAL DEPENDENCY rimraf@2.6.3
│ │ └─┬ UNMET OPTIONAL DEPENDENCY glob@7.1.3
│ │ ├── UNMET OPTIONAL DEPENDENCY fs.realpath@1.0.0
│ │ ├─┬ UNMET OPTIONAL DEPENDENCY inflight@1.0.6
│ │ │ ├── UNMET DEPENDENCY once@1.4.0
│ │ │ └── UNMET DEPENDENCY wrappy@1.0.2
│ │ ├── UNMET DEPENDENCY inherits@2.0.3
│ │ ├── UNMET DEPENDENCY minimatch@3.0.4
│ │ ├─┬ UNMET DEPENDENCY once@1.4.0
│ │ │ └── UNMET DEPENDENCY wrappy@1.0.2
│ │ └── UNMET OPTIONAL DEPENDENCY path-is-absolute@1.0.1
│ ├── UNMET OPTIONAL DEPENDENCY semver@5.6.0
│ └─┬ UNMET OPTIONAL DEPENDENCY tar@4.4.8
│ ├── UNMET OPTIONAL DEPENDENCY chownr@1.1.1
│ ├─┬ UNMET OPTIONAL DEPENDENCY fs-minipass@1.2.5
│ │ └── UNMET DEPENDENCY minipass@2.3.5
│ ├─┬ UNMET DEPENDENCY minipass@2.3.5
│ │ ├── UNMET DEPENDENCY safe-buffer@5.1.2
│ │ └── UNMET DEPENDENCY yallist@3.0.3
│ ├─┬ UNMET OPTIONAL DEPENDENCY minizlib@1.2.1
│ │ └── UNMET DEPENDENCY minipass@2.3.5
│ ├── UNMET DEPENDENCY mkdirp@0.5.1
│ ├── UNMET DEPENDENCY safe-buffer@5.1.2
│ └── UNMET DEPENDENCY yallist@3.0.3
├─┬ glob-parent@3.1.0
│ ├─┬ is-glob@3.1.0
│ │ └── is-extglob@2.1.1 deduped
│ └── path-dirname@1.0.2
├── inherits@2.0.3
├─┬ is-binary-path@1.0.1
│ └── binary-extensions@1.13.1
├─┬ is-glob@4.0.1
│ └── is-extglob@2.1.1
├── normalize-path@3.0.0
├── path-is-absolute@1.0.1
├─┬ readdirp@2.2.1
│ ├── graceful-fs@4.1.15
│ ├── micromatch@3.1.10 deduped
│ └─┬ readable-stream@2.3.6
│ ├── core-util-is@1.0.2
│ ├── inherits@2.0.3 deduped
│ ├── isarray@1.0.0
│ ├── process-nextick-args@2.0.0
│ ├── safe-buffer@5.1.2
│ ├─┬ string_decoder@1.1.1
│ │ └── safe-buffer@5.1.2 deduped
│ └── util-deprecate@1.0.2
└── upath@1.1.2
npm ERR! missing: mkdirp@0.5.1, required by node-pre-gyp@0.10.3
npm ERR! missing: minimist@0.0.8, required by mkdirp@0.5.1
npm ERR! missing: minimatch@3.0.4, required by ignore-walk@3.0.1
npm ERR! missing: brace-expansion@1.1.11, required by minimatch@3.0.4
npm ERR! missing: balanced-match@1.0.0, required by brace-expansion@1.1.11
npm ERR! missing: concat-map@0.0.1, required by brace-expansion@1.1.11
npm ERR! missing: console-control-strings@1.1.0, required by npmlog@4.1.2
npm ERR! missing: inherits@2.0.3, required by readable-stream@2.3.6
npm ERR! missing: safe-buffer@5.1.2, required by readable-stream@2.3.6
npm ERR! missing: safe-buffer@5.1.2, required by string_decoder@1.1.1
npm ERR! missing: console-control-strings@1.1.0, required by gauge@2.7.4
npm ERR! missing: string-width@1.0.2, required by gauge@2.7.4
npm ERR! missing: strip-ansi@3.0.1, required by gauge@2.7.4
npm ERR! missing: code-point-at@1.1.0, required by string-width@1.0.2
npm ERR! missing: is-fullwidth-code-point@1.0.0, required by string-width@1.0.2
npm ERR! missing: strip-ansi@3.0.1, required by string-width@1.0.2
npm ERR! missing: number-is-nan@1.0.1, required by is-fullwidth-code-point@1.0.0
npm ERR! missing: ansi-regex@2.1.1, required by strip-ansi@3.0.1
npm ERR! missing: string-width@1.0.2, required by wide-align@1.1.3
npm ERR! missing: inherits@2.0.3, required by glob@7.1.3
npm ERR! missing: minimatch@3.0.4, required by glob@7.1.3
npm ERR! missing: once@1.4.0, required by glob@7.1.3
npm ERR! missing: once@1.4.0, required by inflight@1.0.6
npm ERR! missing: wrappy@1.0.2, required by inflight@1.0.6
npm ERR! missing: wrappy@1.0.2, required by once@1.4.0
npm ERR! missing: minipass@2.3.5, required by tar@4.4.8
npm ERR! missing: mkdirp@0.5.1, required by tar@4.4.8
npm ERR! missing: safe-buffer@5.1.2, required by tar@4.4.8
npm ERR! missing: yallist@3.0.3, required by tar@4.4.8
npm ERR! missing: minipass@2.3.5, required by fs-minipass@1.2.5
npm ERR! missing: safe-buffer@5.1.2, required by minipass@2.3.5
npm ERR! missing: yallist@3.0.3, required by minipass@2.3.5
npm ERR! missing: minipass@2.3.5, required by minizlib@1.2.1
仔细观察发现 UNMET OPTIONAL DEPENDENCY 的模块和 npm ERR 是同一批模块，也是安装时报 warning 的那些模块。
再仔细观察发现这些都是 fsevents 依赖的模块。
fsevents 只能在 macOS 下安装，无法在 linux 系统安装。linux 下会跳过 fsevents 模块，也不会安装 fsevents 依赖的模块。
这其实算是 npm 的一个 bug，npm i 时报 Warn，npm ls 又报 Err，前后不一致，容易有误解。
目前无论用哪个版本的 npm 都会有这个问题，npm i –no-optional 也不能解决这个问题。
这些报错不影响项目的正常运行，因为 linux 不需要 fsevents。
如果不希望看到 npm Err，可以用 npm i - f 强制安装，安装过程没有 warn，安装完后 npm ls 看下：
└─┬ chokidar@2.1.5
└── fsevents@1.2.7
干净了，没有任何报错。
我的项目是 chokidar 这个模块依赖了 fsevents，chokidar 又是 browser-sync、webpack 等依赖的。
