[英]How to expand an object in an array in JavaScirpt
我正在尝试扩展 JavaScript 中的数组。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 很容易做到这一点,但我想将它与高阶函数一起使用。
我写的代码
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,如果您能额外解释一下double for和高阶函数之间的性能差异,我们将不胜感激。
您可以在测试数组上使用.flatMap()
,在每个designs
数组上使用内部.map()
。 designs 数组中的内部 map 将从当前迭代设计 object 获取属性并将其与父 object 的属性合并。然后可以使用外部.flatMap()
将所有返回的映射连接到一个数组中:
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);
编辑:如果您需要null
值来显示您的设计对象,如果您的设计数组为空,您可以将键显式添加到新的 object 中,当设计数组为空时您可以返回它:
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);
您可以使用Array.reduce
function 和Array.map
来生成数组:
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);
您可以使用高阶 function Array.prototype.reduce()和Array.prototype.map()
const newArr = tests.reduce((prev, {designs, ...current}) => [
...prev, ...designs.map(design => ({...design,...current}));
]
, []);
您的方法和这种高阶方法的性能是相同的,因为Array.prototype.reduce
贯穿整个数组并且只是为我们简化了initialValue
方法。
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