回调函数有问题

Question

所以我有一些这样的代码

const getAPIData = (symbol, callback) => {
  var options = {
    url: "https://api.binance.com/api/v3/ticker/price",
    method: "GET",
    qs: {
      symbol
    },
  };
  request(options, (err, res, body) => {
    body = JSON.parse(body);
    callback(body);
  });
};

var isValid = 0;
getAPIData(symbol, (body) => {
  console.log(body);
  if (body.symbol) {
    console.log("yes");
    isValid = 1;
  } else {
    console.log("no");
  }
});

执行此回调后，无论结果如何，“isValid”变量仍保持为 0。尽管控制台同时记录了 yes 和 no 。调试程序时，isValid 变量仍然为 0。

console.log 函数如何工作而不将 isValid 设置为 1？就像它只是跳过那条线或者我不确定。请帮帮我！

Answer 1

这是异步调用的工作方式。

  var isValid = 0;
  getAPIData(symbol, (body) => {
    console.log(body);
    if (body.symbol) {
      console.log("yes");
      isValid = 1;
      console.log(isValid); // 1
    } else {
      console.log("no");
    }
  });

console.log(isValid); // 0
// when the JS engine gets here, isValid will still be 0
// since getAPIData is asynchronous and it's still in progress at this point
// also, you cannot use any results of getAPIData here