const getURLParameters = url => (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce( (a, v) => ((a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a), {} ); // Examples getURLParameters('http://url.com/page?n=Adam&s=Smith'); // {n: 'Adam', s: 'Smith'} getURLParameters('google.com'); // {}
12.如何将一组表单元素编码为对象？
const formToObject = form => Array.from(new FormData(form)).reduce( (acc, [key, value]) => ({ ...acc, [key]: value }), {} ); // Example formToObject(document.querySelector('#form')); // { email: 'test@email.com', name: 'Test Name' }
Array.from方法用于将两类对象转为真正的数组。类似数组的对象（array-like object）和可遍历（iterable）的对象（包括 ES6 新增的数据结构 Set 和 Map）。
reducer 函数接收4个参数:
Accumulator (acc) (累计器)
Current Value (cur) (当前值)
Current Index (idx) (当前索引)
Source Array (src) (源数组)
13.如何从对象中检索出给定的一组属性？
const get = (from, ...selectors) => [...selectors].map(s => s .replace(/\[([^\[\]]*)\]/g, '.$1.') .split('.') .filter(t => t !== '') .reduce((prev, cur) => prev && prev[cur], from) ); const obj = { selector: { to: { val: 'val to select' } }, target: [1, 2, { a: 'test' }] }; // Example get(obj, 'selector.to.val', 'target[0]', 'target[2].a'); // ['val to select', 1, 'test']
14.延迟调用提供的函数（以毫秒为单位）
const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args); delay( function(text) { console.log(text); }, 1000, 'later' ); // Logs 'later' after one second.
15.如何在给定元素上触发特定事件，并可选地传递自定义数据？
const triggerEvent = (el, eventType, detail) => el.dispatchEvent(new CustomEvent(eventType, { detail })); // Examples triggerEvent(document.getElementById('myId'), 'click'); triggerEvent(document.getElementById('myId'), 'click', { username: 'bob' });
构造方法 CustomerEvent() 创建一个新的 CustomEvent 对象。
CustomEvent 事件是由程序创建的，可以有任意自定义功能的事件。
16.如何从元素中移除事件侦听器？
const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts); const fn = () => console.log('!'); document.body.addEventListener('click', fn); off(document.body, 'click', fn); // no longer logs '!' upon clicking on the page
17.将给定的毫秒数转换为可读格式
const formatDuration = ms => { if (ms < 0) ms = -ms; const time = { day: Math.floor(ms / 86400000), hour: Math.floor(ms / 3600000) % 24, minute: Math.floor(ms / 60000) % 60, second: Math.floor(ms / 1000) % 60, millisecond: Math.floor(ms) % 1000 }; return Object.entries(time) .filter(val => val[1] !== 0) .map(([key, val]) => `${val} ${key}${val !== 1 ? 's' : ''}`) .join(', '); }; // Examples formatDuration(1001); // '1 second, 1 millisecond' formatDuration(34325055574); // '397 days, 6 hours, 44 minutes, 15 seconds, 574 milliseconds'
18.如何得到两个日期之间的差异（以天为单位）
const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24); // Example getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9
19.如何对传递的URL发出GET请求
const httpGet = (url, callback, err = console.error) => { const request = new XMLHttpRequest(); request.open('GET', url, true); request.onload = () => callback(request.responseText); request.onerror = () => err(request); request.send(); }; httpGet( 'https://jsonplaceholder.typicode.com/posts/1', console.log ); // Logs: {"userId": 1, "id": 1, "title": "sample title", "body": "my text"}
20.如何对传递的URL发出POST请求？
const httpPost = (url, data, callback, err = console.error) => { const request = new XMLHttpRequest(); request.open('POST', url, true); request.setRequestHeader('Content-type', 'application/json; charset=utf-8'); request.onload = () => callback(request.responseText); request.onerror = () => err(request); request.send(data); }; const newPost = { userId: 1, id: 1337, title: 'Foo', body: 'bar bar bar' }; const data = JSON.stringify(newPost); httpPost( 'https://jsonplaceholder.typicode.com/posts', data, console.log ); // Logs: {"userId": 1, "id": 1337, "title": "Foo", "body": "bar bar bar"}
21. 如何为指定的选择器创建具有指定范围、步骤和持续时间的计数器？