Matukio ya Map ya JavaScript

new Map() 方法

可以通过将数组传递给 new Map() 构造函数来创建 Map：

mada

// kuzengia Map
const fruits = new Map([
  ["apples", 500],
  ["bananas", 300],
  ["oranges", 200]
]);

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Map.get()

inaonekana kutumia: get() 方法获取 Map 中键的值：

mada

fruits.get("apples");

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Map.set()

inaonekana kutumia: set() 方法向 Map 添加元素：

mada

// kuzengia Map
const fruits = new Map();
// 设置 Map 值
fruits.set("apples", 500);
fruits.set("bananas", 300);
fruits.set("oranges", 200);

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set() 方法也可以用于更改现有的 Map 值：

mada

fruits.set("apples", 500);

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Map.size

size 属性返回 Map 中元素的数量：

mada

fruits.size;

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Map.delete()

delete() 方法移除 Map 中的一个元素：

mada

fruits.delete("apples");

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Map.clear()

clear() 方法移除 Map 中的所有元素：

mada

fruits.clear();

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Map.has()

如果 Map 中存在某个键，has() 方法返回 true：

mada

fruits.has("apples");

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尝试以下代码：

fruits.delete("apples");
fruits.has("apples");

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Map.forEach()

forEach() 方法为 Map 中的每个键值对调用回调函数：

mada

// 列出所有条目
let text = "";
fruits.forEach(function(value, key) {
  text += key + ' = ' + value;
});

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Map.entries()

entries() 方法返回一个包含 Map 中 [key, value] 对的迭代器对象：

mada

// 列出所有条目
let text = "";
for (const x of fruits.entries()) {
  text += x;
}

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Map.keys()

keys() 方法返回一个包含 Map 中键的迭代器对象：

mada

// 列出所有键
let text = "";
for (const x of fruits.keys()) {
  text += x;
}

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Map.values()

values() kitendo kinatoa kipengele cha kuzingatia thamani zote kwenye Map:

mada

// kuzingatia thamani zote
let text = "";
for (const x of fruits.values()) {
  text += x;
}

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inaonekana kutumia: values() kitendo kinasoma thamani za Map:

mada

// kusoma ukubwa wa kila thamani
let total = 0;
for (const x of fruits.values()) {
  total += x;
}

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Orodha kama cheo

Msaada:inabuni ya Map inaonekana kwa kuzengia orodha kama cheo.

mada

// kuzengia orodha
const apples = {name: 'Apples'};
const bananas = {name: 'Bananas'};
const oranges = {name: 'Oranges'};
// kuzengia Map
const fruits = new Map();
// kuingiza element mpya kwenye Map
fruits.set(apples, 500);
fruits.set(bananas, 300);
fruits.set(oranges, 200);

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Kuwa na macho:cheo ni kina (apples), hivyo ni ujumbe ("apples"):

mada

fruits.get("apples"); // inaruhusiwa

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JavaScript Map.groupBy()

ES2024 kinazengia JavaScript Map.groupBy() kitendo.

Map.groupBy() kitendo kinahusisha kugawaza element ya orodha kwa ujumbe wa kirefu wa kugawaza.

Map.groupBy() kitendo kinakutaka orodha orodha ya kuzingatia.

mada

// kuzengia taarifa kwa orodha
const fruits = [
  {name: "apples", quantity: 300},
  {name: "bananas", quantity: 500},
  {name: "oranges", quantity: 200},
  {name: "kiwi", quantity: 150}
];
// muhimu wa kugawaza
function myCallback({ quantity }) {
  return quantity > 200 ? "ok" : "low";
}
// kufaa kwa namba
const result = Map.groupBy(fruits, myCallback);

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Mwongozo wa kivininda

Map.groupBy() Ni jicho la ES2024.

Kuanzia Machi 2024, kila kivininda kirefu kinakubaliwa kwa uwanja huu:

Kadifu ya Object.groupBy() na Map.groupBy()

Object.groupBy() na Map.groupBy() Kadifu ni:

Object.groupBy() Kugawaza mabaki kwenye kipimo cha JavaScript.

Map.groupBy() Kugawaza mabaki kwenye kipimo cha Map.

Mwongozo wa Map kamili

Kwa maelezo kamili, tafadhali nia:Mwongozo wa Map ya JavaScript.

Mwongozo huu inaonekana na maelezo na mifano ya kila mabaki ya Map na matukio.