flow--JS静态类型检查

1.全局安装flow-bin: npm install --global flow-bin
2.切换到工作目录，初始化flow： flow init，它会在当前目录下生成一个.flowconfig文件，内容如下

[ignore]

[include]

[libs]

[lints]

[options]

[strict]

3.flow文件就是将// @flow或 /* @flow */加到js文件的最顶部。只有flow文件，flow进程才会在后台监视这些文件，当有类型检查时，有错误它就会报错
4.新建testFlow.js文件进行测试
测试error案例一：

// @flow
function square(n:number): number {
  return n * n;
}

square('2')

执行flow check，结果如下：

D:\projects\flow-bin>flow check
Found 0 errors

D:\cc\projects\flow-bin>

D:\cc\projects\flow-bin>flow check
Error -------------------------------------------------------------------------------------------------- testFlow.js:6:8

Cannot call `square` with `'2'` bound to `n` because string [1] is incompatible with number [2].

   testFlow.js:6:8
   6| square('2')
             ^^^ [1]

References:
   testFlow.js:2:19
   2| function square(n:number): number {
                        ^^^^^^ [2]



Found 1 error

测试no error案例二：

// @flow
function concat(a: string, b: string) {
  return a + b;
}

concat("A", "B"); // Works!

执行flow check，执行结果如下：

D:\cc\projects\flow-bin>flow check
Found 0 errors