javascript - 如何控制台记录 promise ？

Question

为什么这段代码不能打印任何内容？

预期结果应该是异步结果是:2。但它是0。

"use strict"

// run consoleLogPromise
consoleLogPromise( PromiseAChangeCount() );

// a utility which will always console log any promise 

async function consoleLogPromise(callback) {
  //const res = await callback(); TypeError: callback is not a function
  const res = await callback;
  console.log("async result is: ", res);
}

// a promise returning function
async function PromiseAChangeCount() {
  let count = 0;
  await setTimeout(() => {
    count = 2
  }, 200);
   return count;
}

Answer 1

你必须做这样的事情。返回 PromiseAChangeCount 的 promise 它解析 setTimeout 中的值，然后就可以在consoleLogPromise里面等待了

"use strict"

// run consoleLogPromise
consoleLogPromise(PromiseAChangeCount());

// a utility which will always console log any promise 

async function consoleLogPromise(callback) {
  //const res = await callback(); TypeError: callback is not a function
  const res = await callback;
  console.log("async result is: ", res);
}

// a promise returning function
async function PromiseAChangeCount() {
  let count = 0;
  return new Promise((resolve, _) => {
    setTimeout(() => {
      count = 2;
      resolve(count)
    }, 200);
  })
}