第16题 异步串行 | 异步并行

    // 字节面试题，实现一个异步加法
    function asyncAdd(a, b, callback) {
      setTimeout(function () {
        callback(null, a + b);
      }, 500);
    }
    
    // 解决方案
    // 1. promisify
    const promiseAdd = (a, b) => new Promise((resolve, reject) => {
      asyncAdd(a, b, (err, res) => {
        if (err) {
          reject(err)
        } else {
          resolve(res)
        }
      })
    })
    
    // 2. 串行处理
    async function serialSum(...args) {
      return args.reduce((task, now) => task.then(res => promiseAdd(res, now)), Promise.resolve(0))
    }
    
    // 3. 并行处理
    async function parallelSum(...args) {
      if (args.length === 1) return args[0]
      const tasks = []
      for (let i = 0; i < args.length; i += 2) {
        tasks.push(promiseAdd(args[i], args[i + 1] || 0))
      }
      const results = await Promise.all(tasks)
      return parallelSum(...results)
    }
    
    // 测试
    (async () => {
      console.log('Running...');
      const res1 = await serialSum(1, 2, 3, 4, 5, 8, 9, 10, 11, 12)
      console.log(res1)
      const res2 = await parallelSum(1, 2, 3, 4, 5, 8, 9, 10, 11, 12)
      console.log(res2)
      console.log('Done');
    })()