javascript - 仅在定义时分配属性

Question

我有以下变量:

const quote = {
    author: req.body.author,
    quote: req.body.quote,
    source: req.body.source,
    updatedAt: Date.now(),
  };

我只想分配已定义的值。例如，我可以检查是否未定义:

 if(req.body.author === undefined) {
    console.log('author undefined');
  }

但是我如何将其转化为不赋值呢？如果 undefined，我是否需要事后检查然后删除该属性？

Answer 1

如果属性在发布数据中未定义，你能不能只使用默认值并将它们设置为空？

//Unsure if you want the default value to have any meaning
//using null would likely achieve what you're asking.
var default_value = null;

const quote = {
    author: req.body.author || default_value,
    quote: req.body.quote || default_value,
    source: req.body.source || default_value,
    updatedAt: Date.now(),
};

如果你真的想去除它们，这里有一个你可以在之后使用的基本循环。

for (var i in quote) {
       if (quote[i] == default_value) {
           //Unsure how this works with const... might have to change to var
           delete quote[i];
       }
   }

或者，您可以遍历 req.body 对象，避免在初始声明后进行验证。

var quote = {};

for (var i in req.body) {
    quote[i] = req.body[i];
}

不确定您是否仍要针对 req.body 对象中的某些值进行验证，以便您可以添加检查它们是否为 null/undefined

var quote = {};

for (var i in req.body) {

   //This will only declare the value on the quote object if the value
   //is not null or undefined. False could be a value you're after so
   //I avoided using the cleaner version of 'if (!req.body[i]) ...'
   if (req.body[i] !== null || req.body[i] !== undefined) { 
      quote[i] = req.body[i];
   }
}

你甚至可以把它分解成一个很好的可重用函数(下面的基本实现):

//Obj would be your post data
//bad_values would be an array of values you're not interested in.
function validatePOST (obj, bad_values) {

     var data = {};

     for (var i in obj) {

         //Check the value isn't in the array of bad values
         if (bad_values.indexOf(obj[i]) === -1) {

             data[i] = obj[i];
         }
     }

     //Return the validated object
     return data;
}

现在您可以在所有 route 使用它。

var quote = validatePOST(req.body, [null, undefined]);