Node.js中的Array.forEach是否異步？

Question

數組上的forEach是否異步？ 糖果是一系列糖果對象。

app.get('/api/:id',function(req, res){

  console.log("Get candy");
  var id = req.params.id;

  candies.forEach( function(candy, index){
    if(candy.id == id){
      console.log("Candy found. Before return");
      return res.json(candy);
      console.log("Candy found. After return");
    }
  });

  console.log("Print error message");
  return res.json({error: "Candy not found"});
});

在控制台中，我得到

[nodemon] starting `node app.js`
listning on port 3000
Get candy
Candy found. Before return
Print error message
Error: Can't set headers after they are sent.
   at ServerResponse.setHeader (_http_outgoing.js:367:11)
   ....

這是最近的變化嗎？ 自從我完成了node.js以來已經有一段時間了

Answer 1

Can't set headers after they are sent.您將收到“ Can't set headers after they are sent. 例外，因為您嘗試返回兩次響應（可能），一次是在candies.forEach ， candies.forEach一次是在路線的最后一行。 還要注意， return后的任何代碼都不會執行。

這是您如何重寫以避免錯誤的方法-

app.get('/api/:id',function(req, res){

    console.log("Get candy");
    var id = req.params.id;
    var foundCandy = false;
    candies.forEach( function(candy, index){
        if(candy.id == id){
            foundCandy = true;
            console.log("Candy found. Before return");
        }
    });

    if (foundCandy) {
        return res.json(candy);
    } else {
        return res.json({error: "Candy not found"});
    }
});

Answer 2

您可以使用Array.filter找到糖果。

app.get('/api/:id', function(req, res) {

  console.log("Get candy");
  var id = req.params.id;

  var result = candies.filter(candy => candy.id == id);

  if (result.length) {
    return res.json(result[0]);
  } else {
    console.log("Print error message");
    return res.json({
      error: "Candy not found"
    });
  }
});