Node.js中的Array.forEach是異步的嗎？

Question

是forEach上的數組異步？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"}); 
}); 

在控制檯中我得到

[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？已經過了一段時間了，因爲我已經完成了node.js

Answer 1

你會得到Can't set headers after they are sent.異常，因爲你試圖在candies.forEach之內兩次返回響應（可能），並且再次返回路由的最後一行。還請注意，return之後的任何代碼都不會被執行。

這裏是你如何把它改寫，以避免錯誤 -

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" 
    }); 
    } 
});