36 * n frequently used JavaScript function fragments in work

Time:2020-11-14

Recently, I saw an article about 36 JavaScript function fragments commonly used in our work.

As an interviewer (█▀█), how can you have only one answer?

Array

Array de duplication

Scheme 1:Set + ...

function noRepeat(arr) {
  return [...new Set(arr)];
}
noRepeat([1,2,3,1,2,3])

Scheme 2:Set + Array.from

function noRepeat(arr) {
  return Array.from(new Set(arr));
}
noRepeat([1,2,3,1,2,3])

Scheme 3: Double traversal comparison subscript

function noRepeat(arr) {
  return arr.filter((v, idx)=>idx == arr.lastIndexOf(v))
}
noRepeat([1,2,3,1,2,3])

Scheme 4: single traversal + object feature

The property of object is that the key will not be repeated.
Values are used here because the type can be preserved and keys will become a string.

function noRepeat(arr) {
  return Object.values(arr.reduce((s,n)=>{
    s[n] = n;
    return s
  },{}))
}
noRepeat([1,2,3,1,2,3])

Postscript

For the above scheme, there are other variants.

Find array maximum

Scheme 1:Math.max + ...

function arrayMax(arr) {
  return Math.max(...arr);
}
arrayMax([-1,-4,5,2,0])

Scheme 2:Math.max + apply

function arrayMax(arr) {
  return Math.max.apply(Math, arr)
}
arrayMax([-1,-4,5,2,0])

Scheme 3:Math.max+Traversal

function arrayMax(arr) {
  return arr.reduce((s,n)=>Math.max(s, n))
}
arrayMax([-1,-4,5,2,0])

Scheme 4: comparison, conditional operation + traversal

function arrayMax(arr) {
  return arr.reduce((s,n)=>s>n?s:n)
}
arrayMax([-1,-4,5,2,0])

Scheme 5: sequencing

function arrayMax(arr) {
  return arr.sort((n,m)=>m-n)[0]
}
arrayMax([-1,-4,5,2,0])

Find array minimum

ditto,I don’t understand why it’s divided into two topics

  1. Math.maxchange intoMath.min
  2. s>n?s:nchange intos<n?s:n
  3. (n,m)=>m-nchange into(n,m)=>n-mOr take the last element directly

Returns the original array split by an array of size

Scheme 1: Array.from + slice

function chunk(arr, size = 1) {
  return Array.from(
    {
      length: Math.ceil(arr.length / size),
    },
    (v, i) => arr.slice(i * size, i * size + size)
  );
}
chunk([1,2,3,4,5,6,7,8],3)

Scheme 2: Array.from + splice

function chunk(arr, size = 1) {
  return Array.from(
    {
      length: Math.ceil(arr.length / size),
    },
    (v, i) => arr.splice(0, size)
  );
}
chunk([1,2,3,4,5,6,7,8],3)

Scheme 3: traversal + Split

function chunk(arr, size = 1) {
    var _returnArr = [];
    while(arr.length){
        _returnArr.push(arr.splice(0, size))
    }
    return _returnArr
}
chunk([1,2,3,4,5,6,7,8],3)

Check the number of times an element in the array appears

Scheme 1: reduce

function countOccurrences(arr, value) {
  return arr.reduce((a, v) => (v === value ? a + 1 : a + 0), 0);
}
countOccurrences([1,2,3,4,5,1,2,1,2,3], 1)

Scheme 2: filter

function countOccurrences(arr, value) {
  return arr.filter(v=>v===value).length
}
countOccurrences([1,2,3,4,5,1,2,1,2,3], 1)

Flatten array

Scheme 1: recursion +

function flatten(arr, depth = -1) {
  if (depth === -1) {
    return [].concat(
      ...arr.map((v) => (Array.isArray(v) ? this.flatten(v) : v))
    );
  }
  if (depth === 1) {
    return arr.reduce((a, v) => a.concat(v), []);
  }
  return arr.reduce(
    (a, v) => a.concat(Array.isArray(v) ? this.flatten(v, depth - 1) : v),
    []
  );
}
flatten([1,[2,[3]]])

Scheme 2: ES6 native flat

function flatten(arr, depth = Infinity) {
  return arr.flat(depth)
}
flatten([1,[2,[3]]])

Compares two arrays and returns different elements

Scheme 1: filter + includes

There are some problems in his original text4,5No return

function diffrence(arrA, arrB) {
  return arrA.filter((v) => !arrB.includes(v));
}
diffrence([1,2,3], [3,4,5,2])

You need to do it again

function diffrence(arrA, arrB) {
  return arrA.filter((v) => !arrB.includes(v))
    .concat(arrB.filter((v) => !arrA.includes(v)));
}
diffrence([1,2,3], [3,4,5,2])

Scheme two: hash + traversal

It’s a variant of scheme 1. It’s optimizedincludesPerformance.

Returns the same element in two arrays

Scheme 1: filter + includes

function intersection(arr1, arr2) {
  return arr2.filter((v) => arr1.includes(v));
}
intersection([1,2,3], [3,4,5,2])

Scheme 2: hash for homomorphic variants

function intersection(arr1, arr2) {
    var set = new Set(arr2)
  return arr1.filter((v) => set.has(v));
}
intersection([1,2,3], [3,4,5,2])

Remove n elements from the right

Scheme 1: slice

function dropRight(arr, n = 0) {
  return n < arr.length ? arr.slice(0, arr.length - n) : [];
}
dropRight([1,2,3,4,5], 2)

Scheme 2: split

function dropRight(arr, n = 0) {
  return arr.splice(0, arr.length - n)
}
dropRight([1,2,3,4,5], 2)

Scheme 3: slice

function dropRight(arr, n = 0) {
  return arr.slice(0, -n)
}
dropRight([1,2,3,4,5], 2)

Scheme 4: modify the length

function dropRight(arr, n = 0) {
    arr.length = Math.max(arr.length - n, 0)
    return arr
}
dropRight([1,2,3,4,5], 2)

Intercepts the first eligible element and subsequent elements

Scheme 1: slice + cycle

function dropElements(arr, fn) {
  while (arr.length && !fn(arr[0])) arr = arr.slice(1);
  return arr;
}
dropElements([1,2,3,4,5,1,2,3], (v) => v == 2)

Scheme 2: FindIndex + slice

function dropElements(arr, fn) {
  return arr.slice(Math.max(arr.findIndex(fn), 0));
}
dropElements([1,2,3,4,5,1,2,3], (v) => v === 3)

Scheme 3: split + cycle

function dropElements(arr, fn) {
  while (arr.length && !fn(arr[0])) arr.splice(0,1);
  return arr;
}
dropElements([1,2,3,4,5,1,2,3], (v) => v == 2)

Returns the element of the array with the subscript interval nth

Scheme 1: filter

function everyNth(arr, nth) {
  return arr.filter((v, i) => i % nth === nth - 1);
}
everyNth([1,2,3,4,5,6,7,8], 2)

Scheme 2: modification of judgment conditions for scheme 1

function everyNth(arr, nth) {
  return arr.filter((v, i) => (i+1) % nth === 0);
}
everyNth([1,2,3,4,5,6,7,8], 2)

Returns the nth element in an array (negative numbers are supported)

Scheme 1: slice

function nthElement(arr, n = 0) {
  return (n >= 0 ? arr.slice(n, n + 1) : arr.slice(n))[0];
}
nthElement([1,2,3,4,5], 0)
nthElement([1,2,3,4,5], -1)

Scheme 2: ternary operator

function nthElement(arr, n = 0) {
  return (n >= 0 ? arr[0] : arr[arr.length + n])
}
nthElement([1,2,3,4,5], 0)
nthElement([1,2,3,4,5], -1)

Returns the array header element

Scheme 1:

function head(arr) {
  return arr[0];
}
head([1,2,3,4])

Scheme 2:

function head(arr) {
  return arr.slice(0,1)[0];
}
head([1,2,3,4])

Returns the element at the end of an array

Scheme 1:

function last(arr) {
  return arr[arr.length - 1];
}

Scheme 2:

function last(arr) {
  return arr.slice(-1)[0];
}
last([1,2,3,4,5])

Array shuffling

Scheme one: shuffling algorithm

function shuffle(arr) {
  let array = arr;
  let index = array.length;

  while (index) {
    index -= 1;
    let randomInedx = Math.floor(Math.random() * index);
    let middleware = array[index];
    array[index] = array[randomInedx];
    array[randomInedx] = middleware;
  }

  return array;
}
shuffle([1,2,3,4,5])

Scheme 2: sort + random

function shuffle(arr) {
  return arr.sort((n,m)=>Math.random() - .5)
}
shuffle([1,2,3,4,5])

Convert pseudo array to array

Scheme 1: Array.from

Array.from({length: 2})

Scheme 2: prototype.slice

Array.prototype.slice.call({length: 2,1:1})

Scheme 3: prototype.splice

Array.prototype.splice.call({length: 2,1:1},0)

Browser object BOM

Determine whether the browser supports CSS properties

/**
 *Informs the browser of the specified CSS properties supported
 *The @ param {string} key - CSS property is the name of the attribute and does not need to be prefixed
 *@ returns {string} - supported properties
 */
function validateCssKey(key) {
  Const jskey = tocamelcase (key); // some CSS attributes are formed by hyphens
  if (jsKey in document.documentElement.style) {
    return key;
  }
  let validKey = "";
  //The property name is the form of prefix in JS, and the property value is the form of prefix in CSS
  //After trying, WebKit is also a lowercase WebKit
  const prefixMap = {
    Webkit: "-webkit-",
    Moz: "-moz-",
    ms: "-ms-",
    O: "-o-",
  };
  for (const jsPrefix in prefixMap) {
    const styleKey = toCamelCase(`${jsPrefix}-${jsKey}`);
    if (styleKey in document.documentElement.style) {
      validKey = prefixMap[jsPrefix] + key;
      break;
    }
  }
  return validKey;
}

/**
 *Convert the string with hyphenation into the string of hump nomenclature
 */
function toCamelCase(value) {
  return value.replace(/-(\w)/g, (matched, letter) => {
    return letter.toUpperCase();
  });
}

/**
 *Check whether the browser supports a CSS property value (ES6 version)
 *@ param {string} key - the CSS property name of the property value to be checked
 *@ param {string} value - CSS property value to check (without prefix)
 *@ returns {string} - returns the property values supported by the browser
 */
function valiateCssValue(key, value) {
  const prefix = ["-o-", "-ms-", "-moz-", "-webkit-", ""];
  const prefixValue = prefix.map((item) => {
    return item + value;
  });
  const element = document.createElement("div");
  const eleStyle = element.style;
  //The application of each prefix, and finally the application of no prefix, depends on what happens to the browser
  //This is the last element that's best in prefix, which is' '
  prefixValue.forEach((item) => {
    eleStyle[key] = item;
  });
  return eleStyle[key];
}

/**
 *Check whether the browser supports a CSS property value
 *@ param {string} key - the CSS property name of the property value to be checked
 *@ param {string} value - CSS property value to check (without prefix)
 *@ returns {string} - returns the property values supported by the browser
 */
function valiateCssValue(key, value) {
  var prefix = ["-o-", "-ms-", "-moz-", "-webkit-", ""];
  var prefixValue = [];
  for (var i = 0; i < prefix.length; i++) {
    prefixValue.push(prefix[i] + value);
  }
  var element = document.createElement("div");
  var eleStyle = element.style;
  for (var j = 0; j < prefixValue.length; j++) {
    eleStyle[key] = prefixValue[j];
  }
  return eleStyle[key];
}

function validCss(key, value) {
  const validCss = validateCssKey(key);
  if (validCss) {
    return validCss;
  }
  return valiateCssValue(key, value);
}

https://segmentfault.com/a/11…
It has foreach in it.

Return to current page address

Scheme 1: Location

function currentURL() {
  return window.location.href;
}
currentURL()

Scheme 2: a label

function currentURL() {
  var el = document.createElement('a')
  el.href = ''
  return el.href
}
currentURL()

Get scroll bar position

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

Get the parameters in the URL

Scheme 1: regular + reduce

function getURLParameters(url) {
  return url
    .match(/([^?=&]+)(=([^&]*))/g)
    .reduce(
      (a, v) => (
        (a[v.slice(0, v.indexOf("="))] = v.slice(v.indexOf("=") + 1)), a
      ),
      {}
    );
}
getURLParameters(location.href)

Scheme 2: split + reduce

function getURLParameters(url) {
  return url
    . split ('?') // access? division
    . slice (1) // no first part
    . join() // splicing
    . split ('&') / & split
    . map (v = > v. split ('=')) // = split
    .reduce((s,n)=>{s[n[0]] = n[1];return s},{})
}
getURLParameters(location.href)
// getURLParameters('')

Scheme 3: urlsearchparams

Page Jump, is it recorded in history

Scheme 1:

function redirect(url, asLink = true) {
  asLink ? (window.location.href = url) : window.location.replace(url);
}

Scheme 2:

function redirect(url, asLink = true) {
  asLink ? window.location.assign(url) : window.location.replace(url);
}

Scroll bar back to top animation

Scheme 1: C – C / 8

C has no definition

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

After amendment

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

Copy text

Scheme 1:

function copy(str) {
  const el = document.createElement("textarea");
  el.value = str;
  el.setAttribute("readonly", "");
  el.style.position = "absolute";
  el.style.left = "-9999px";
  el.style.top = "-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);
  }
}

Scheme 2: cliboard.js

Type of testing equipment

Scheme 1: UA

function detectDeviceType() {
  return /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(
    navigator.userAgent
  )
    ? "Mobile"
    : "Desktop";
}
detectDeviceType()

Scheme 2: Event Attributes

function detectDeviceType() {
  return ("ontouchstart" in window || navigator.msMaxTouchPoints)
    ? "Mobile"
    : "Desktop";
}
detectDeviceType()

Cookie

increase

function setCookie(key, value, expiredays) {
  var exdate = new Date();
  exdate.setDate(exdate.getDate() + expiredays);
  document.cookie =
    key +
    "=" +
    escape(value) +
    (expiredays == null ? "" : ";expires=" + exdate.toGMTString());
}

Delete

function delCookie(name) {
  var exp = new Date();
  exp.setTime(exp.getTime() - 1);
  var cval = getCookie(name);
  if (cval != null) {
    document.cookie = name + "=" + cval + ";expires=" + exp.toGMTString();
  }
}

check

function getCookie(name) {
  var arr,
    reg = new RegExp("(^| )" + name + "=([^;]*)(;|$)");
  if ((arr = document.cookie.match(reg))) {
    return arr[2];
  } else {
    return null;
  }
}

empty

Sometimes we want to empty, but we can’t get all the cookies.
At this time, we can use the method of filling and then clearing.

Date

Timestamp to time

  • The default is the current time conversion result
  • Isms is whether the timestamp is Ms
function timestampToTime(timestamp = Date.parse(new Date()), isMs = true) {
  const date = new Date(timestamp * (isMs ? 1 : 1000));
  return `${date.getFullYear()}-${
    date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1
  }-${date.getDate()} ${date.getHours()}:${date.getMinutes()}:${date.getSeconds()}`;
}
  1. Pad start can be changed to pad start
  2. The complement can also be changed to slice
    36 * n frequently used JavaScript function fragments in work

If I do overseas, there will be some problems. Generally, I use moment to solve them. If you want to see the original

Gets the current timestamp

Based on the previous question

Scheme 1: Date.parse (new Date())

Scheme 2: Date.now ()

Scheme 3 + new date ()

Document object DOM

Fixed scroll bar

/**
 *Function Description: some business scenarios, such as the pop-up box, need to prohibit page scrolling. This is a solution compatible with Android and IOS
 */

let scrollTop = 0;

function preventScroll() {
  //Store current scroll position
  scrollTop = window.scrollY;

  //The scrollable area is fixed and cannot be rolled when the height of the scrollable area is 0
  document.body.style["overflow-y"] = "hidden";
  document.body.style.position = "fixed";
  document.body.style.width = "100%";
  document.body.style.top = -scrollTop + "px";
  // document.body.style['overscroll-behavior'] = 'none'
}

function recoverScroll() {
  document.body.style["overflow-y"] = "auto";
  document.body.style.position = "static";
  // document.querySelector('body').style['overscroll-behavior'] = 'none'

  window.scrollTo(0, scrollTop);
}

Determine whether the current position is at the bottom of the page

  • The return value is true / false
function bottomVisible() {
  return (
    document.documentElement.clientHeight + window.scrollY >=
    (document.documentElement.scrollHeight ||
      document.documentElement.clientHeight)
  );
}

Determine whether the element is visible

  • Partiallyvisible is whether it is fully visible or not
function elementIsVisibleInViewport(el, partiallyVisible = false) {
  const { top, left, bottom, right } = el.getBoundingClientRect();

  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;
}

Get element CSS Style

function getStyle(el, ruleName) {
  return getComputedStyle(el, null).getPropertyValue(ruleName);
}

Enter full screen

function launchFullscreen(element) {
  if (element.requestFullscreen) {
    element.requestFullscreen();
  } else if (element.mozRequestFullScreen) {
    element.mozRequestFullScreen();
  } else if (element.msRequestFullscreen) {
    element.msRequestFullscreen();
  } else if (element.webkitRequestFullscreen) {
    element.webkitRequestFullScreen();
  }
}

launchFullscreen(document.documentElement);
launchFullscreen( document.getElementById ("Id"); // an element enters the full screen

Exit full screen

function exitFullscreen() {
  if (document.exitFullscreen) {
    document.exitFullscreen();
  } else if (document.msExitFullscreen) {
    document.msExitFullscreen();
  } else if (document.mozCancelFullScreen) {
    document.mozCancelFullScreen();
  } else if (document.webkitExitFullscreen) {
    document.webkitExitFullscreen();
  }
}

exitFullscreen();

Full screen events

document.addEventListener("fullscreenchange", function (e) {
  if (document.fullscreenElement) {
    console.log ("enter full screen");
  } else {
    console.log ("exit full screen");
  }
});

Number

Digital thousand percentile segmentation

function commafy(num) {
  return num.toString().indexOf(".") !== -1
    ? num.toLocaleString()
    : num.toString().replace(/(\d)(?=(?:\d{3})+$)/g, "$1,");
}
commafy(1000)

Generating random numbers

function randomNum(min, max) {
  switch (arguments.length) {
    case 1:
      return parseInt(Math.random() * min + 1, 10);
    case 2:
      return parseInt(Math.random() * (max - min + 1) + min, 10);
    default:
      return 0;
  }
}
randomNum(1,10)

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36 * n frequently used JavaScript function fragments in work