# compose

## Compose

<https://github.com/reduxjs/redux/blob/master/src/compose.js>

```javascript
function compose(...funcs) {
  if (funcs.length === 0) {
    return arg => arg
  }

  if (funcs.length === 1) {
    return funcs[0]
  }

  return funcs.reduce((a, b) => (...args) => a(b(...args)))
}
```

使用

```
let a = (c) => c * c
let b = (x) => x + x
compose(a, b)(1)
// 4
```

> 因為 compose(a, b)(1) 會變為 `a(b(1))`

## 如果HOC要用在compose內必須要這樣寫

```javascript
export default function withRules(ruleOptions = {}) {
  return Component =>
    class WithRules extends React.Component {
      render() {
        return (
          <Component>
           ....
         </Component>
        )
      }
    }
}
```

> ```
> (opt) => (BaseComponent) => return class
> ```