初心者が学ぶflowtype入門 Ver.1.0 ref: https://qiita.com/ikkitang/items/8c22b93fc4d7ca166495

.flowconfig

[ignore]
+ .*/node_modules/.*

[include]

[libs]

[lints]

[options]

[strict]

app.js

// @flow

let message = 'flowType';
message = 2;
console.log("Hello! " + message);

app.ts

let value : number = 1;
let str : string = "1";

if (value == str) {
    console.log("同じ");
} else {
    console.log("違う");
}

file0.txt

# node 環境を作成
$ npm init -y
# flowtypeをinstall
$ npm install --save flowtype flow-bin

file11.txt

$ npm run-script flow check

Error ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ src/app.js:5:5

Cannot compare number [1] to string [2].

 [1] 2│ let value : number = 1;
 [2] 3│ let str : string = "1";
     4│
     5│ if (value == str) {
     6│     console.log("同じ");
     7│ } else {
     8│     console.log("違う");

file4.txt

# ルートディレクトリ上で実行.
$ npm run-script flow check

> flowtype-sample@1.0.0 flow /Users/hogehoge/flowtype-sample
> flow "check"

Found 0 errors

file5.txt

$ node src/app.js
Hello! Node.js × flowtype

file8.txt

~~

Error ┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈ src/app.js:4:11

Cannot assign 2 to message because number [1] is incompatible with string [2].

     1│ // @flow
     2│
 [2] 3│ let message: string = 'flowType';
 [1] 4│ message = 2;
     5│ console.log("Hello! " + message);


〜〜

package.json

{
  "name": "flowtype-sample",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1",
+    "flow": "flow"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "flow-bin": "^0.74.0",
    "flowtype": "^2.0.0"
  }
}