Shulou(Shulou.com)06/03 Report--

This article mainly introduces the front-end development of which commonly used JS function, the article introduces in great detail, has a certain reference value, interested friends must read it!

25. Unique: array is deduplicated and a new array is returned

Function unique (arr) {if (! isArrayLink (arr)) {/ / is not a class array object return arr} let result = [] let objarr = [] let obj = Object.create (null) arr.forEach (item = > {if (isStatic (item) {/ / is the raw data let key = item +'_'+ getRawType (item) except symbol If (! obj [key]) {obj [key] = true result.push (item)}} else {/ / reference type and symbol if (! objarr.includes (item)) {objarr.push (item) result.push (item)}}) return resulte}

26. Simple implementation of Set

Window.Set = window.Set | | (function () {function Set (arr) {this.items = arr? Unique (arr): []; this.size = size of this.items.length; / / Array} Set.prototype = {add: function (value) {/ / add an element. If the element already exists, skip it and return the Set structure itself. If (! this.has (value)) {this.items.push (value); this.size++;} return this;}, clear: function () {/ / clears all members with no return value. This.items = [] this.size = 0}, delete: function (value) {/ / delete a value and return a Boolean value indicating whether the deletion is successful. Return this.items.some ((v, I) = > {if (v = value) {this.items.splice (iMagne1) return true} return false})}, has: function (value) {/ / returns a Boolean value Indicates whether the value is a member of Set. Return this.items.some (v = > v = value)}, values: function () {return this.items},} return Set;} ()

27. Repeat: generate a duplicate string consisting of n str, which can be modified to fill an array, etc.

Function repeat (str, n) {let res ='; while (n) {if (n% 2 = 1) {res + = str;} if (n > 1) {str + = str;} n > > = 1;} return res}; / / repeat ('123) = > 123123123

28. DateFormater: formatting time

Function dateFormater (formater, t) {let date = t? New Date (t): new Date (), Y = date.getFullYear () +', M = date.getMonth () + 1, D = date.getDate (), H = date.getHours (), m = date.getMinutes (), s = date.getSeconds () Return formater.replace (/ YYYY | yyyy/g,Y). Replace (/ YY | yy/g,Y.substr (2Magazine 2)) .replace (/ MM/g, (M / June 26, 2019 / / dateStrForma ('June 26, 2019', 'YYYY mm month DD date' 'YYYYMMDD') = > 20190626Universe / regular can also be used to implement / /' June 26th, 2019'. Replace (/ (\ d {4}) year (\ d {2}) month (\ d {2}) day /,'$1murf / 2murf 3') = > 2019-06-26

30. GetPropByPath: get the object attribute according to the string path: 'obj [0] .count'

Function getPropByPath (obj, path, strict) {let tempObj = obj; path = path.replace (/\ [(\ w+)\] / g,'.$ 1'); / / convert [0] to .0 path = path.replace (/ ^\ /,''); / / remove the beginning. Let keyArr = path.split ('.'); / / according to. Cut let I = 0; for (let len = keyArr.length; I

< len - 1; ++i) { if (!tempObj && !strict) break; let key = keyArr[i]; if (key in tempObj) { tempObj = tempObj[key]; } else { if (strict) {//开启严格模式，没找到对应key值，抛出错误 throw new Error('please transfer a valid prop path to form item!'); } break; } } return { o: tempObj, //原始数据 k: keyArr[i], //key值 v: tempObj ? tempObj[keyArr[i]] : null // key值对应的值 };}; 31、GetUrlParam：获取Url参数，返回一个对象 function GetUrlParam(){ let url = _document.location.toString(); let arrObj = url.split("?"); let params = Object.create(null) if (arrObj.length >

1) {arrObj = arrObj [1] .split ("&"); arrObj.forEach (item= > {item= item.split ("="); params [item [0]] = item [1]})} return params;} / /? a=1&b=2&c=3 = > {a: "1", b: "2", c: "3"}

32. DownloadFile:base64 data export file, file download

Function downloadFile (filename, data) {let DownloadLink = document.createElement ('a'); if (DownloadLink) {document.body.appendChild (DownloadLink); DownloadLink.style = 'display: none';DownloadLink.download = filename;DownloadLink.href = data;if (document.createEvent) {let DownloadEvt = document.createEvent (' MouseEvents'); DownloadEvt.initEvent ('click', true, false); DownloadLink.dispatchEvent (DownloadEvt);} else if (document.createEventObject) {DownloadLink.fireEvent (' onclick') } else if (typeof DownloadLink.onclick = = 'function') {DownloadLink.onclick ();} document.body.removeChild (DownloadLink);}}

33. ToFullScreen: full screen

Function toFullScreen () {let elem = document.body; elem.webkitRequestFullScreen? Elem.webkitRequestFullScreen (): elem.mozRequestFullScreen? Elem.mozRequestFullScreen (): elem.msRequestFullscreen? Elem.msRequestFullscreen (): elem.requestFullScreen? Elem.requestFullScreen (): alert ("browser does not support full screen");}

34. ExitFullscreen: exit full screen

Function exitFullscreen () {let elem = parent.document;elem.webkitCancelFullScreen? Elem.webkitCancelFullScreen (): elem.mozCancelFullScreen? Elem.mozCancelFullScreen (): elem.cancelFullScreen? Elem.cancelFullScreen (): elem.msExitFullscreen? Elem.msExitFullscreen (): elem.exitFullscreen? Elem.exitFullscreen (): alert ("failed to switch, try Esc to quit");}

35. RequestAnimationFrame:window animation

Window.requestAnimationFrame = window.requestAnimationFrame | | window.webkitRequestAnimationFrame | | window.mozRequestAnimationFrame | | window.msRequestAnimationFrame | | window.oRequestAnimationFrame | | function (callback) {/ / to make the effect of setTimteout as close as possible to 60 frames per second window.setTimeout (callback, 1000 / 60);} window.cancelAnimationFrame = window.cancelAnimationFrame | | window.webkitCancelAnimationFrame | window.mozCancelAnimationFrame | | window.msCancelAnimationFrame | window.oCancelAnimationFrame | | function (id) {/ / to make setTimteout's effect as close to 60 frames per second as possible window.clearTimeout (id);}

36. _ isNaN: check whether the data is non-numeric

Function _ isNaN (v) {return! (typeof v = = 'string' | | typeof v =' number') | | isNaN (v)}

37. Max: find the maximum value in the non-NaN data in the array

Function max (arr) {arr = arr.filter (item = >! _ isNaN (item)) return arr.length? Math.max.apply (null, arr): undefined} / / max ([1, 2,'11, null, 'fdf', []]) = > 11

38. Min: find the minimum value in non-NaN data in the array

Function min (arr) {arr = arr.filter (item = >! _ isNaN (item)) return arr.length? Math.min.apply (null, arr): undefined} / / min ([1, 2,'11, null, 'fdf', []]) = > 1

39. Random: returns a random number directly from lower-upper. (lower, upper, no matter positive or negative or small, but must be non-NaN data)

Function random (lower, upper) {lower = + lower | | 0upper = + upper | | 0return Math.random () * (upper-lower) + lower;} / / random (0,0.5) = > 0.3567039135734613//random (2,1) = > 1.6718418553475423//random (- 2,-1) = >-1.4474325452361945

40. Object.keys: returns an array of enumerable properties of a given object

Object.keys = Object.keys | | function keys (object) {if (object = null | | object = undefined) {throw new TypeError ('Cannot convert undefined or null to object');} let result = []; if (isArrayLike (object) | | isPlainObject (object)) {for (let key in object) {object.hasOwnProperty (key) & & (result.push (key)}} return result;})

41. Object.values: returns an array of all enumerable attribute values of a given object itself

Object.values = Object.values | | function values (object) {if (object = null | | object = undefined) {throw new TypeError ('Cannot convert undefined or null to object');} let result = []; if (isArrayLike (object) | | isPlainObject (object)) {for (let key in object) {object.hasOwnProperty (key) & (result.push (objectkey))}} return result;}

42. Arr.fill: fill the array with the value value, starting at the start position and ending at the end position (but excluding the end position), returning the original array

Array.prototype.fill = Array.prototype.fill | | function fill (value, start, end) {let ctx = this let length = ctx.length; start = parseInt (start) if (isNaN (start)) {start = 0} else if (start)

< 0) { start = -start >

Length? 0: (length + start);} end = parseInt (end) if (isNaN (end) | | end > length) {end = length} else if (end)

< 0) { end += length; } while (start < end) { ctx[start++] = value; } return ctx;}//Array(3).fill(2) ===>

[2, 2, 2]

43. Arr.includes: used to determine whether an array contains a specified value. If true is returned, otherwise false is returned, you can specify the location to start the query.

Array.prototype.includes = Array.prototype.includes | | function includes (value, start) {let ctx = this;let length = ctx.length;start = parseInt (start) if (isNaN (start)) {start = 0} else if (start)

< 0) {start = -start >

Length? 0: (length + start);} let index = ctx.indexOf (value); return index > = start;}

44. Returns the value of the first element in the array that passes the test (judged in the function fn)

Array.prototype.find = Array.prototype.find | | function find (fn, ctx) {ctx = ctx | | this;let result;ctx.some ((value, index, arr), thisValue) = > {return fn (value, index, arr)? (result = value, true): false}) return result}

45. Arr.findIndex: returns the subscript of the first element in the array that passes the test (judged in the function fn)

Array.prototype.findIndex = Array.prototype.findIndex | | function findIndex (fn, ctx) {ctx = ctx | | this let result; ctx.some ((value, index, arr), thisValue) = > {return fn (value, index, arr)? (result = index, true): false}) return result}

46. Performance.timing: performance analysis using performance.timing

_ window.onload = function () {setTimeout (function () {let t = performance.timing) Console.log ('DNS query time:' + (t.domainLookupEnd-t.domainLookupStart). ToFixed (0)) console.log ('TCP link time:' + (t.connectEnd-t.connectStart). ToFixed (0)) console.log ('request request time:' + (t.responseEnd-t.responseStart). ToFixed (0) console.log ('time spent parsing dom tree:' + (t.domComplete-t) .domInteractive) .toFixed (0) console.log ('white screen time:' + (t.responseStart-t.navigationStart) .toFixed (0)) console.log ('domready time:' + (t.domContentLoadedEventEnd-t.navigationStart) .toFixed (0)) console.log ('onload time:' + (t.loadEventEnd-t.navigationStart). ToFixed (0)) if (t = performance.memory) {console.log ('js memory usage ratio:'+ (t.usedJSHeapSize / t.totalJSHeapSize * 100) .tofixed (2) +'%'}})})}

47. Prohibit certain keyboard events

Document.addEventListener ('keydown' Function (event) {return! (1212 = = event.keyCode | | / prohibit F1123 = = event.keyCode | | / prohibit F12event.ctrlKey & & 82 = = event.keyCode | | / prohibit ctrl+Revent.ctrlKey & & 18 = = event.keyCode | | / prohibit ctrl+Nevent.shiftKey & & 18 = = event.keyCode | | / prohibit shift+F10event.altKey & & 115 = = event.keyCode | | / prohibit alt+F4 "A" = = event.srcElement.tagName & & event.shiftKey// prohibit shift+ from clicking on the a tag) | | (event.returnValue = false)})

48. Right-click, select and copy are prohibited

['contextmenu',' selectstart', 'copy'] .forEach (function (ev) {document.addEventListener (ev, function (event) {return event.returnValue = false;})); these are all the contents of the article "what are the commonly used JS functions in front-end development? thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

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