any消除技巧

1. 数组拍平函数

function flat(arr: Array<any>): Array<any> {
  const result = []
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] instanceof Array) {
      result.push(...arr[i])
    } else {
      result.push(arr[i])
    }
  }
  return result
}

function flat<T>(arr:  Array<T | T[]>) {
  const result: T[] = []
  for (let i = 0; i < arr.length; i++) {
    if (arr[i] instanceof Array) {
      result.push(...arr[i] as T[])
    } else {
      result.push(arr[i] as T)
    }
  }
  return result
}

2. 类型守卫

Promise.all(newPromise).then((results: Array<[string, string]>) => {
    // results = [['username', undefined], ['password', 'too long']]
    callback(zip(results.filter<[string, string]>(item => !!item[1])))
  })

上面的代码我们filter里面接受的类型肯定是我们最后的返回值类型，而我们最后是要返回[string, string]的，但是她又说我们必须得是一个predicate，所以我们需要单独写一个类型守卫

// item有可能是[string, undefined]也有可能是[string, string]，返回的这个item的类型是[string, string]，然后返回item[1]的类型是string
function isError(item: [string, undefined] | [string, string]): item is [string, string] {
    return typeof item[1] === 'string'
  }
  Promise.all(newPromise).then((results: Array<[string, string]>) => {
    // results = [['username', undefined], ['password', 'too long']]
    callback(zip(results.filter<[string, string]>(isError)))
  })