如何在 JavaScirpt 中擴展數組中的 object

Question

我正在嘗試擴展 JavaScript 中的數組。object ↓

const tests = [
    {
        id: 1,
        name: 'taro',
        designs: [
            {
                designId: 1,
                designName: "design1"
            },
            {
                designId: 2,
                designName: "design2"
            }
        ]
    },
    {
        id: 2,
        name: 'John',
        designs: [
            {
                designId: 3,
                designName: "design3"
            },
            {
                designId: 4,
                designName: "design4"
            }
        ]
    },
{
        id: 3,
        name: 'Lisa',
        designs: []
    },
];

[
  { id: 1, name: 'taro', designId: 1, designName: 'design1' },
  { id: 1, name: 'taro', designId: 2, designName: 'design2' },
  { id: 2, name: 'John', designId: 3, designName: 'design3' },
  { id: 2, name: 'John', designId: 4, designName: 'design4' },
  { id: 3, name: 'Lisa', designId: null, designName: null },
]

使用 double for 很容易做到這一點，但我想將它與高階函數一起使用。

我寫的代碼

for (let i = 0; i < tests.length; i++) {
    for (let j = 0; j < tests[i].designs.length; j++) {
        const id = tests[i].id
        const name = tests[i].name
        result.push({
            id,
            name,
            designId: tests[i].designs[j].designId,
            designName: tests[i].designs[j].designName
        })
    }
}

另外，如果您能額外解釋一下double for和高階函數之間的性能差異，我們將不勝感激。

Answer 1

您可以在測試數組上使用.flatMap() ，在每個designs數組上使用內部.map() 。 designs 數組中的內部 map 將從當前迭代設計 object 獲取屬性並將其與父 object 的屬性合並。然后可以使用外部.flatMap()將所有返回的映射連接到一個數組中：

 const tests = [ { id: 1, name: 'taro', designs: [ { designId: 1, designName: "design1" }, { designId: 2, designName: "design2" } ] }, { id: 2, name: 'John', designs: [ { designId: 3, designName: "design3" }, { designId: 4, designName: "design4" } ] }, ]; const res = tests.flatMap(({designs, ...rest}) => designs.map(design => ({...rest, ...design }))); console.log(res);

編輯：如果您需要null值來顯示您的設計對象，如果您的設計數組為空，您可以將鍵顯式添加到新的 object 中，當設計數組為空時您可以返回它：

 const tests = [ { id: 1, name: 'taro', designs: [] }, { id: 2, name: 'John', designs: [] }, ]; const res = tests.flatMap(({designs, ...rest}) => designs.length? designs.map(design => ({...rest, ...design })): {...rest, designId: null, designName: null} ); console.log(res);

Answer 2

您可以使用Array.reduce function 和Array.map來生成數組：

const results = tests.reduce((acc, { designs, ...rest }) => [
  ...acc,
  ...designs.map(e => ({ ...rest, ...e }))
], []);

 const tests = [ { id: 1, name: 'taro', designs: [ { designId: 1, designName: "design1" }, { designId: 2, designName: "design2" } ] }, { id: 2, name: 'John', designs: [ { designId: 3, designName: "design3" }, { designId: 4, designName: "design4" } ] }, ]; const results = tests.reduce((acc, { designs, ...rest }) => [...acc, ...designs.map(e => ({...rest, ...e })) ], []); console.log(results);

Answer 3

您可以使用高階 function Array.prototype.reduce()和Array.prototype.map()

const newArr = tests.reduce((prev, {designs, ...current}) => [
   ...prev, ...designs.map(design => ({...design,...current}));
]      
, []);

您的方法和這種高階方法的性能是相同的，因為Array.prototype.reduce貫穿整個數組並且只是為我們簡化了initialValue方法。