map類型特點與創建方法：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"> <style> </style></head><body> <script> // 對象的鍵名會自動轉為字符串 // let obj = { // 1: 'cyy1', // '1': 'cyy2' // }; // console.log(obj); // 對象的鍵名是對象時，會自動轉為字符串 // 讀取時也要先轉為字符串再讀取 // let obj = { // name: 'cyy' // }; // let obj2 = { // obj: 'cyy2', // [obj]: 'cyy3' // }; // console.log(obj2); // console.log(obj2[obj.toString()]); // map類型，什么都可以作為鍵，鍵名可以是任何類型 // let map = new Map(); // map.set('name', 'cyy'); // map.set(function() {}, 'cyy2'); // map.set({}, 'cyy3'); // map.set(1, 'cyy4'); // console.log(map); // 構造函數創建時加入數據 let map = new Map([ ['name', 'cyy'], ['age', 18] ]); console.log(map); // 支持鏈式操作 let str = 'cyy'; let str2 = str.toUpperCase().substr(1, 2); console.log(str2); map.set('11', 11).set('22', 22); console.log(map); </script></body></html> |
map類型增刪改查操作：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"> <style> </style></head><body> <script> let obj = { name: 'cyy' }; let map = new Map(); map.set(obj, 'obj'); console.log(map.has(obj)); console.log(map); console.log(map.get(obj)); console.log(map.delete('abc')); console.log(map.delete(obj)); map.clear(); console.log(map); </script></body></html> |
遍歷map類型數據：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"> <style> </style></head><body> <script> let map = new Map([ [1, 11], [2, 22] ]); // console.log(map.keys()); // console.log(map.values()); // console.log(map.entries()); // for (let k of map.keys()) { // console.log(k); // } // for (let v of map.values()) { // console.log(v); // } // for (let e of map.entries()) { // console.log(e); // } // for (let [k, v] of map.entries()) { // console.log(`${k}--${v}`); // } map.forEach((item, key) => { console.log(item + '--' + key); }) </script></body></html> |
map類型轉換操作：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"> <style> </style></head><body> <script> let map = new Map([ ['name', 'cyy'], ['age', '18'] ]); // console.log(...map); // console.log([...map]); // console.log([...map.entries()]); // console.log([...map.keys()]); // console.log([...map.values()]); // let arr = [...map].filter(item => item[1].includes('cyy')); let arr = [...map].filter(item => { return item[1].includes('cyy'); }); // console.log(arr); let new_map = new Map(arr); console.log(new_map); console.log(new_map.values()); // ...是展開語法 console.log(...new_map.values()); </script></body></html> |
map類型管理DOM節點：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"> <style> </style></head><body> <div name="cyy1">cyy1</div> <div name="cyy2">cyy2</div> <script> let map = new Map(); let divs = document.querySelectorAll('div'); divs.forEach(item => { // 往map中壓入數據 map.set(item, { content: item.getAttribute('name') }); }); // console.log(map); map.forEach((config, elem) => { // console.log(config, elem); elem.addEventListener('click', function() { console.log(config.content); }); }) </script></body></html> |
使用map類型控制網站表單提交：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"> <style> </style></head><body> <form action="#" onsubmit="return post()"> 接受協議： <input type="checkbox" name="agreement" error="請接受協議"> 我是學生： <input type="checkbox" name="student" error="網站只對學生開放"> <input type="submit" value="提交"> </form> <script> function post() { let map = new Map(); let inputs = document.querySelectorAll('[error]'); console.log(inputs); inputs.forEach(item => { map.set(item, { error: item.getAttribute('error'), status: item.checked }); }); // console.log(map); return [...map].every(([elem, config]) => { // 短路操作，前面為真，則不會執行后面 // 前面會假，則執行后面 config.status || alert(config.error); return config.status; // console.log(config); }); } </script></body></html> |
WeakMap的語法使用：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <meta name="viewport" content="width=device-width,minimum-scale=1.0,maximum-scale=1.0,user-scalable=no"> <style> </style></head><body> <div>cyy</div> <div>cyy2</div> <script> // WeakMap的鍵只能是引用對象 // let map = new WeakMap(); // map.set('name'); // console.log(map); // map.set([]); // console.log(map); // let map = new WeakMap(); // let divs = document.querySelectorAll('div'); // divs.forEach(item => map.set(item, item.innerHTML)); // console.log(map); // WeakMap也是弱引用類型 // let arr = []; // let map = new WeakMap(); // map.set(arr, 'cyy'); // map.delete(arr); // console.log(map.has(arr)); // console.log(map); // 弱引用類型，values、keys、entries、迭代循環都用不了 let map = new WeakMap(); // console.log(map.keys()); for (const iterator of map) { console.log(iterator); } </script></body></html> |
WeakMap弱引用類型體驗：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css"> <style> </style></head><body> <script> let a = { name: 'cyy' }; let b = a; let map = new WeakMap(); map.set(a, 'cuu2'); console.log(map); a = null; b = null; console.log(map); setTimeout(function () { console.log(map); }, 1000); </script></body></html> |
使用WeakMap開發選課組件：
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<!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Document</title> <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css"> <style> * { margin: 0; padding: 0; box-sizing: border-box; } main { width: 100%; display: flex; flex: 1; } section { border: 2px solid #ddd; width: 50%; padding: 10px; } ul { list-style: none; } li { padding: 10px; border: 2px solid orange; margin-bottom: 5px; position: relative; } a { display: inline-block; position: absolute; right: 10px; width: 20px; height: 20px; background: green; color: white; text-decoration: none; line-height: 20px; text-align: center; } #list span { background: green; border-radius: 5px; padding: 5px; color: white; margin: 5px; } #list { margin-top: 20px; } </style></head><body> <main> <section> <ul> <li><span>html</span><a href="javascript:;">＋</a></li> <li><span>css</span><a href="javascript:;">＋</a></li> <li><span>js</span><a href="javascript:;">＋</a></li> </ul> </section> <section> <strong id="count">共選了2門課</strong> <p id="list"> <!-- <span>111</span> --> </p> </section> </main> <script> class Lesson { // 構造函數 constructor() { this.lis = document.querySelectorAll('li'); this.countElem = document.getElementById('count'); this.listElem = document.getElementById('list'); // console.log(this.lis, this.countElem, this.listElem); this.map = new WeakMap(); } run() { this.lis.forEach(li => { li.querySelector('a').addEventListener('click', event => { let a = event.target; // console.log(li); // console.log(event.target.parentElement); const state = li.getAttribute('select'); if (state) { // 移除 li.removeAttribute('select'); this.map.delete(li); a.style.backgroundColor = 'green'; a.innerHTML = '＋'; } else { // 添加 li.setAttribute('select', true); this.map.set(li); a.style.backgroundColor = 'red'; a.innerHTML = '-'; } // console.log(this.map); this.render(); }); }) } render() { this.countElem.innerHTML = `共選了${this.count()}門課`; // console.log(this.count()); this.listElem.innerHTML = this.list(); } count() { return [...this.lis].reduce((count, li) => { return count += this.map.has(li) ? 1 : 0; }, 0); } list() { let lis = [...this.lis].filter(li => { return this.map.has(li); }).map(li => { return `<span>${li.querySelector('span').innerHTML}</span>`; }).join(''); // console.log(lis); return lis; } } new Lesson().run(); </script></body></html> |
到此這篇關于Map與WeakMap類型在JavaScript中的使用的文章就介紹到這了,更多相關Map與WeakMap類型在JavaScript中的使用內容請搜索服務器之家以前的文章或繼續瀏覽下面的相關文章希望大家以后多多支持服務器之家！
原文鏈接：https://www.cnblogs.com/chenyingying0/archive/2020/11/17/13995123.html
