JS--解决常见JavaScript问题的代码片段

1. 如何获取URL？

const getBaseURL = url => url.replace(/[?#].*$/, '');

getBaseURL('http://url.com/page?name=Adam&surname=Smith');
// 'http://url.com/page'

2. 如何检查URL是否是绝对的？

const isAbsoluteURL = str => /^[a-z][a-z0-9+.-]*:/.test(str);

isAbsoluteURL('https://google.com'); // true
isAbsoluteURL('ftp://www.myserver.net'); // true
isAbsoluteURL('/foo/bar'); // false

3. 如何获取URL参数作为对象？

const getURLParameters = url =>
  (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce(
    (a, v) => (
      (a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1)), a
    ),
    {}
  );

getURLParameters('google.com'); // {}
getURLParameters('http://url.com/page?name=Adam&surname=Smith');
// {name: 'Adam', surname: 'Smith'}

4. 如何检查元素是否包含另一个元素？

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

elementContains(
  document.querySelector('head'),
  document.querySelector('title')
);
// true
elementContains(document.querySelector('body'), document.querySelector('body'));

5.如何获取元素的所有祖先？

const getAncestors = el => {
  let ancestors = [];
  while (el) {
    ancestors.unshift(el);
    el = el.parentNode;
  }
  return ancestors;
};

getAncestors(document.querySelector('nav'));
// [document, html, body, header, nav]

6. 如何平滑滚动元素到视图中？

const smoothScroll = element =>
  document.querySelector(element).scrollIntoView({
    behavior: 'smooth'
  });

smoothScroll('#fooBar'); // scrolls smoothly to the element with the id fooBar
smoothScroll('.fooBar');
// scrolls smoothly to the first element with a class of fooBar

7. 如何处理元素外的点击？

const onClickOutside = (element, callback) => {
  document.addEventListener('click', e => {
    if (!element.contains(e.target)) callback();
  });
};

onClickOutside('#my-element', () => console.log('Hello'));
// Will log 'Hello' whenever the user clicks outside of #my-element

8. 如何生成UUID？

const UUIDGeneratorBrowser = () =>
  ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
    (
      c ^
      (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))
    ).toString(16)
  );

UUIDGeneratorBrowser(); // '7982fcfe-5721-4632-bede-6000885be57d'

9. 如何获取选中的文本？

const getSelectedText = () => window.getSelection().toString();
getSelectedText(); // 'Lorem ipsum'

10.如何复制文本到剪贴板？

const copyToClipboard = str => {
  if (navigator && navigator.clipboard && navigator.clipboard.writeText)
    return navigator.clipboard.writeText(str);
  return Promise.reject('The Clipboard API is not available.');
};

11. 如何给HTML元素添加样式？

const addStyles = (el, styles) => Object.assign(el.style, styles);

addStyles(document.getElementById('my-element'), {
  background: 'red',
  color: '#ffff00',
  fontSize: '3rem'
});

12. 如何切换全屏模式？

const fullscreen = (mode = true, el = 'body') =>
  mode
    ? document.querySelector(el).requestFullscreen()
    : document.exitFullscreen();

fullscreen(); // Opens `body` in fullscreen mode
fullscreen(false); // Exits fullscreen mode

13. 如何检测Caps Lock是否打开？

<form>
  <label for="username">Username:</label>
  <input id="username" name="username">

  <label for="password">Password:</label>
  <input id="password" name="password" type="password">
  <span id="password-message" style="display: none">Caps Lock is on</span>
</form>
const el = document.getElementById('password');
const msg = document.getElementById('password-message');

el.addEventListener('keyup', e => {
  msg.style = e.getModifierState('CapsLock')
    ? 'display: block'
    : 'display: none';
});

14. 如何检查日期是否有效？

const isDateValid = (...val) => !Number.isNaN(new Date(...val).valueOf());

isDateValid('December 17, 1995 03:24:00'); // true
isDateValid('1995-12-17T03:24:00'); // true
isDateValid('1995-12-17 T03:24:00'); // false
isDateValid('Duck'); // false
isDateValid(1995, 11, 17); // true
isDateValid(1995, 11, 17, 'Duck'); // false
isDateValid({}); // false

15. 如何从 Date 中获取冒号时间？

const getColonTimeFromDate = date => date.toTimeString().slice(0, 8);

getColonTimeFromDate(new Date()); // '08:38:00'

16. 如何查看当前用户的首选语言？

const detectLanguage = (defaultLang = 'en-US') =>
  navigator.language ||
  (Array.isArray(navigator.languages) && navigator.languages[0]) ||
  defaultLang;

detectLanguage(); // 'nl-NL'

17. 如何查看用户喜欢的配色方案？

const prefersDarkColorScheme = () =>
  window &&
  window.matchMedia &&
  window.matchMedia('(prefers-color-scheme: dark)').matches;

prefersDarkColorScheme(); // true

18. 如何检查设备是否支持触摸事件？

const supportsTouchEvents = () =>
  window && 'ontouchstart' in window;

supportsTouchEvents(); // true

19. URL对象

const url = new URL("https://example.com/login?user=someguy&page=news");

url.origin
// "https://example.com"
url.host
// "example.com"
url.protocol
// "https:"
url.pathname
// "/login"
url.searchParams.get('user')
// "someguy"