Object.groupBy()
静态方法根据提供的回调函数返回的字符串值对给定可迭代对象中的元素进行分组。返回的对象具有每个组的单独属性，其中包含组中的元素的数组。
js
const inventory = [
{ name: 'asparagus', type: 'vegetables', quantity: 5 },
{ name: 'bananas', type: 'fruit', quantity: 0 },
{ name: 'goat', type: 'meat', quantity: 23 },
{ name: 'cherries', type: 'fruit', quantity: 5 },
{ name: 'fish', type: 'meat', quantity: 22 },
]
// 根据元素的 type 属性的值对元素进行分组
const result = Object.groupBy(inventory, ({ type }) => type)
console.log(result)
/* Result is:
{
vegetables: [
{ name: 'asparagus', type: 'vegetables', quantity: 5 },
],
fruit: [
{ name: 'bananas', type: 'fruit', quantity: 0 },
{ name: 'cherries', type: 'fruit', quantity: 5 }
],
meat: [
{ name: 'goat', type: 'meat', quantity: 23 },
{ name: 'fish', type: 'meat', quantity: 22 }
]
}
*/js
const inventory = [
{ name: 'asparagus', type: 'vegetables', quantity: 5 },
{ name: 'bananas', type: 'fruit', quantity: 0 },
{ name: 'goat', type: 'meat', quantity: 23 },
{ name: 'cherries', type: 'fruit', quantity: 5 },
{ name: 'fish', type: 'meat', quantity: 22 },
]
// 根据 quantity 字段的值将项目分为不同分组(sufficient/restock)。
function myCallback({ quantity }) {
return quantity > 5 ? 'sufficient' : 'restock'
}
const result2 = Object.groupBy(inventory, myCallback)
console.log(result)
/* Result is:
{
restock: [
{ name: 'asparagus', type: 'vegetables', quantity: 5 },
{ name: 'bananas', type: 'fruit', quantity: 0 },
{ name: 'cherries', type: 'fruit', quantity: 5 }
],
sufficient: [
{ name: 'goat', type: 'meat', quantity: 23 },
{ name: 'fish', type: 'meat', quantity: 22 }
]
}
*/Map.groupBy()
Map.groupBy() 静态方法使用提供的回调函数返回的值对给定可迭代对象中的元素进行分组。最终返回的 Map 使用测试函数返回的唯一值作为键，可用于获取每个组中的元素组成的数组。
该方法主要用于对与对象相关的元素进行分组，特别是当该对象可能随时间而变化时。如果对象不变，你可以使用字符串表示它，并使用 Object.groupBy() 分组元素。
js
const inventory = [
{ name: 'asparagus', type: 'vegetables', quantity: 5 },
{ name: 'bananas', type: 'fruit', quantity: 0 },
{ name: 'goat', type: 'meat', quantity: 23 },
{ name: 'cherries', type: 'fruit', quantity: 5 },
{ name: 'fish', type: 'meat', quantity: 22 },
]
const restock = { restock: true }
const sufficient = { restock: false }
const result = Map.groupBy(inventory, ({ quantity }) =>
quantity < 6 ? restock : sufficient,
)
console.log(result.get(restock))
/* Result is:
[
{ name: 'asparagus', type: 'vegetables', quantity: 5 },
{ name: 'bananas', type: 'fruit', quantity: 0 },
{ name: 'cherries', type: 'fruit', quantity: 5 },
]
*/
console.log(result.get(sufficient))
/* Result is:
[
{ name: 'goat', type: 'meat', quantity: 23 },
{ name: 'fish', type: 'meat', quantity: 22 },
]
*/