Question

我正在使用Object.assign()将值复制到对象：

const { one, two, three } = attributes;

return Object.assign( props, { 
  "data-one": one,
  "data-two": two,
  "data-three": three   
} );

如果属性的值为空，则返回undefined。我希望它返回一个空字符串，或者理想情况下不复制任何空属性。

我试过了：

const { one, two, three } = attributes;

var oneValue = one ? one : "";
var twoValue = two ? two : "";
var threeValue = three ? three : "";

return Object.assign( props, { 
  "data-one": oneValue,
  "data-two": twoValue,
  "data-three": threeValue   
} );

它的工作原理是发送空值而不是未定义，但似乎不是很花哨。有没有更好的方法来解决这个问题？

Answer 1

您可以在使用解构时定义默认值。

const attributes = { one: 'one' };
const { one = '', two = '', three = '' } = attributes;
const props = {}

console.log(Object.assign( props, { 
  "data-one": one,
  "data-two": two,
  "data-three": three
}));

最后，如果你有很多共同的行为，你可以命名你要复制的属性并写一个循环。

Answer 2

@CyberJunkie ，您可以使用对象销毁的概念进行修复，如下所示：

注意：访问Destructuring assignment和Destructuring assignment - Mozilla.org's documentation，了解销毁对象。

function getObj(attributes)
{
	const { one: newOne = '', two: newTwo = '', three: newThree = '' } = attributes;

	// var oneValue = one ? one : "";
	// var twoValue = two ? two : "";
	// var threeValue = three ? three : "";
	var props = {four: "The four", six: "The six"};

	return Object.assign( props, { 
	  "data-one": newOne,
	  "data-two": newTwo,
	  "data-three": newThree  
	} );
}

var prettyObj = JSON.stringify(getObj({one: "ObjData1.1", two: 'ObjData2', three: 'ObjData3'}), null, 4);
console.log(prettyObj)
/*
	{
	    "four": "The four",
	    "six": "The six",
	    "data-one": "ObjData1.1",
	    "data-two": "ObjData2",
	    "data-three": "ObjData3"
	}
*/

prettyObj = JSON.stringify(getObj({one: "ObjData1.2", two: 'ObjData2'}), null, 4);
console.log(prettyObj)
/*
	{
	    "four": "The four",
	    "six": "The six",
	    "data-one": "ObjData1.2",
	    "data-two": "ObjData2",
	    "data-three": ""
	}
*/

prettyObj = JSON.stringify(getObj({one: "ObjData1.2"}), null, 4)
console.log(prettyObj)
/*
	{
	    "four": "The four",
	    "six": "The six",
	    "data-one": "ObjData1.2",
	    "data-two": "",
	    "data-three": ""
	}
*/

最后，您可以查看我在 NODE REPL 上执行的代码，因为它显示了const { one: newOne = '', two: newTwo = '', three: newThree = '' } = attributes;和const { one = '', two = '', three = '' } = attributes;语句之间的差异。

H:\RishikeshAgrawani\Projects\Stk\UndefinedValue>node
>
> // Example 1
undefined
>
> attributes = {one: "ObjData1.2", two: 'ObjData2'}
{ one: 'ObjData1.2', two: 'ObjData2' }
>
> const { one: newOne = '', two: newTwo = '', three: newThree = '' } = attributes;
undefined
>
> one
ReferenceError: one is not defined
>
> newOne
'ObjData1.2'
>
> newTwo
'ObjData2'
>
> newThree
''
>
> // Example 2
undefined
> attributes2 = {one: "ObjData1.2", two: 'ObjData2'}
{ one: 'ObjData1.2', two: 'ObjData2' }
>
> const { one = '', two = '', three = '' } = attributes;
undefined
> one
'ObjData1.2'
> two
'ObjData2'
> three
''
>

感谢。

Answer 3

 function assignNotUndefined(target, obj) {
   for(const key of Object.keys(obj)) {
    if(obj[key] !== undefined)
     target[key] = obj[key];
   }
   return target;
 }

可用作：

const { one, two, three } = attributes;

return assignNotUndefined( props, { 
 "data-one": one,
 "data-two": two,
 "data-three": three   
});

JS将未定义的值转换为空字符串

3 个答案: