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24 modern ES6 code snippets ​

24 modern ES6 code snippets to solve practical JS problems

单纯一味地学习 JavaScript 语法，相关知识点若不快速加以使用和实践，很快就会忘记，跟没学一样。这篇文章，是从网络一篇文章上找来的 24 段代码，仔细学习代码中涉及到不熟悉的知识点。

隐藏元素 ​

js
const hide = (...el) => [...el].forEach((e) => (e.style.display = "none"));

// Example
hide(document.querySelectorAll("img")); // Hides all <img> elements on the page

知识点 1 ​

  • 箭头函数 - 基础知识
  • 解构赋值
  • forEach() 方法：
    • 语法：array.forEach(callbackFn(currentValue, index, arr), thisValue)
    • 用法：forEach() 方法用于调用数组的每个元素，并将元素传递给回调函数

检查指定类 ​

js
const hasClass = (el, className) => el.classList.contains(className);

// Example
hasClass(document.querySelector("p.special"), "special"); // true
  1. How to toggle a class for an element?
js
const toggleClass = (el, className) => el.classList.toggle(className);

// Example
toggleClass(document.querySelector("p.special"), "special");
// The paragraph will not have the 'special' class anymore

4.How to get the scroll position of the current page?

js
const getScrollPosition = (el = window) => ({
  x: el.pageXOffset !== undefined ? el.pageXOffset : el.scrollLeft,
  y: el.pageYOffset !== undefined ? el.pageYOffset : el.scrollTop,
});

// Example
getScrollPosition(); // {x: 0, y: 200}

5.How to smooth-scroll to the top of the page?

js
const scrollToTop = () => {
  const c = document.documentElement.scrollTop || document.body.scrollTop;
  if (c > 0) {
    window.requestAnimationFrame(scrollToTop);
    window.scrollTo(0, c - c / 8);
  }
};

// Example
scrollToTop();

6.How to check if the parent element contains the child element?

js
const elementContains = (parent, child) =>
  parent !== child && parent.contains(child);

// Examples
elementContains(
  document.querySelector("head"),
  document.querySelector("title")
);
// true
elementContains(document.querySelector("body"), document.querySelector("body")); // false

7.How to check if the element specified is visible in the viewport?

js
const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
  const { top, left, bottom, right } = el.getBoundingClientRect();
  const { innerHeight, innerWidth } = window;
  return partiallyVisible
    ? ((top > 0 && top < innerHeight) ||
        (bottom > 0 && bottom < innerHeight)) &&
        ((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
    : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};

// Examples
elementIsVisibleInViewport(el); // (not fully visible)
elementIsVisibleInViewport(el, true); // (partially visible)

8.How to fetch all images within an element?

js
const getImages = (el, includeDuplicates = false) => {
  const images = [...el.getElementsByTagName("img")].map((img) =>
    img.getAttribute("src")
  );
  return includeDuplicates ? images : [...new Set(images)];
};

// Examples
getImages(document, true); // ['image1.jpg', 'image2.png', 'image1.png', '...']
getImages(document, false); // ['image1.jpg', 'image2.png', '...']

9.How to figure out if the device is a mobile device or a desktop/laptop?

js
const detectDeviceType = () =>
/Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent)
? 'Mobile'
: 'Desktop';

// Example
detectDeviceType(); // "Mobile" or "Desktop"

10.How to get the current URL?

js
const currentURL = () => window.location.href;

// Example
currentURL(); // 'https://google.com'
11.How to create an object containing the parameters of the current URL?
```js
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.How to encode a set of form elements as an object?

js
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' }

13.How to retrieve a set of properties indicated by the given selectors from an object?

js
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.How to invoke the provided function after wait (in milliseconds)?

js
const delay = (fn, wait, ...args) => setTimeout(fn, wait, ...args);
delay(
function(text) {
console.log(text);
},
1000,
'later'
);

// Logs 'later' after one second.

15.How to trigger a specific event on a given element, optionally passing custom data?

js
const triggerEvent = (el, eventType, detail) =>
el.dispatchEvent(new CustomEvent(eventType, { detail }));

// Examples
triggerEvent(document.getElementById('myId'), 'click');
triggerEvent(document.getElementById('myId'), 'click', { username: 'bob' });

16.How to remove an event listener from an element?

js
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.How to get readable format of the given number of milliseconds?

js
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.How to get the difference (in days) between two dates?

js
const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
(dateFinal - dateInitial) / (1000 _ 3600 _ 24);

// Example
getDaysDiffBetweenDates(new Date('2017-12-13'), new Date('2017-12-22')); // 9
19.How to make a GET request to the passed URL?

```js
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.How to make a POST request to the passed URL?

js
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.How to create a counter with the specified range, step and duration for the specified selector?

js
const counter = (selector, start, end, step = 1, duration = 2000) => {
let current = start,
\_step = (end - start) \* step < 0 ? -step : step,
timer = setInterval(() => {
current += \_step;
document.querySelector(selector).innerHTML = current;
if (current >= end) document.querySelector(selector).innerHTML = end;
if (current >= end) clearInterval(timer);
}, Math.abs(Math.floor(duration / (end - start))));
return timer;
};

// Example
counter('#my-id', 1, 1000, 5, 2000); // Creates a 2-second timer for the element with id="my-id"

22.How to copy a string to the clipboard?

js
const copyToClipboard = (str) => {
  const el = document.createElement("textarea");
  el.value = str;
  el.setAttribute("readonly", "");
  el.style.position = "absolute";
  el.style.left = "-9999px";
  document.body.appendChild(el);
  const selected =
    document.getSelection().rangeCount > 0
      ? document.getSelection().getRangeAt(0)
      : false;
  el.select();
  document.execCommand("copy");
  document.body.removeChild(el);
  if (selected) {
    document.getSelection().removeAllRanges();
    document.getSelection().addRange(selected);
  }
};

// Example
copyToClipboard("Lorem ipsum"); // 'Lorem ipsum' copied to clipboard.

23.How to find out if the browser tab of the page is focused?

js
const isBrowserTabFocused = () => !document.hidden;

// Example
isBrowserTabFocused(); // true

24.How to create a directory, if it does not exist?

js
const fs = require("fs");
const createDirIfNotExists = (dir) =>
  !fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined;

// Example
createDirIfNotExists("test"); // creates the directory 'test', if it doesn't exist