前端魔法堂：屏蔽Backspace致使頁面回退

時間 2019-12-05

標籤前端屏蔽 backspace 致使頁面回退简体版

原文原文鏈接

前言

前幾天用戶反映在錄入資料時一不當心錯按Backspace鍵，就會直接回退到是一個頁面，致使以前辛辛苦苦錄入的資料所有丟失了。哦？竟然還有這種狀況。下面咱們來一塊兒探討一下吧！html

Windows系統下獨有的行爲

Windows下的IE、FireFox和Chrome 52以前的瀏覽器，當焦點不在一個可編輯的元素上時，按Backspace鍵就會回退到上一個頁面，按Shift+Backspace鍵則會前進到下一個頁面。
而Chrome 52之後的瀏覽器則屏蔽了Backspace和Shift+Backspace的上述行爲，而是採用Alt+Left實現回退和Alt+Right實現前進。若是想恢復Backspace回退，則須要安裝Go Back With Backspace的Extension才行。
對於FireFox而言，咱們能夠設置Backspace和Shift+Backspace的行爲。瀏覽器

在地址欄輸入about:configapp
在搜索框輸入browser.backspace_action，而後設置項目值便可。有3個可選項
0，表示Backspace和Shift+Backspace的行爲對應頁面回退和前進(Windows下的默認值)dom

1，表示Backspace和Shift+Backspace的行爲對應頁面向下滾動和向上滾動
2或其餘值，表示不響應Backspace和Shift+Backspace(Ubuntu16下的默認值)ide

注意：Linux和OS X下的瀏覽器按Backspace和Shift+Backspace不會觸發頁面的回退和前進。函數

如何應對

方案一：頁面跳轉時彈出二次確認

經過beforeunload事件實現頁面跳轉時彈出二次確認模態窗，讓用戶有後悔的機會。但會截斷其餘正常跳轉的操做流暢性，在確實沒有辦法時才使用！ui

方案二：直接屏蔽

屏蔽Backspace和Shift+Backspace的默認行爲，僅當焦點落在可編輯區域中時才暫時取消屏蔽。
那麼哪些算是能得到焦點的可編輯區域呢？就下面這些咯！！url

input[type=text]:not([readonly])
input[type=password]:not([readonly])
input[type=number]:not([readonly])
input[type=email]:not([readonly])
input[type=url]:not([readonly])
input[type=search]:not([readonly])
input[type=tel]:not([readonly])
textarea:not([readonly])
[contenteditable]:not([readonly])

就是說當焦點落在上述符合規則的元素上時，按Backspace和Shift+Backspace的默認行爲就不是頁面跳轉，所以不用屏蔽掉。spa

附加功能

如今咱們的目的是頁面不會由於用戶誤操做而刷新，致使頁面數據丟失。這裏有兩個組合鍵一樣會的致使頁面刷新prototype

ctrl+r刷新當前頁面，可被阻止;
ctrl+w關閉當前窗體或標籤頁，沒法阻止。

代碼時間.js

;window.nobsgb || (function(exports){
                var started = false
                exports.start = function(){started = true}
                exports.stop = function(){started = false}

        var KEYCODE = {
            BACKSPACE: 8,
            R: 82
        }
        // 判斷type是否不受阻止
        var isEscapableType = function(rEscapableTypes){
            return function(type){
                return rEscapableTypes.test(type)
            }
        }(/text|textarea|tel|email|number|search|password|url/i)
        // 判斷標籤是否不受阻止
        var isEscapableTag = function(rEscapableTag){
            return function(tag){
                return rEscapableTag.test(tag)
            }
        }(/input|textarea/i)
        // 判斷是否設置爲content editable
        var isContentEditable = function(el){
            return el.isContentEditable
        }
        // 判斷是否爲不受阻止的Backspace
        var isEscapableBackspace = function(el){
            return or(isEscapableTag(el.tagName)
                      && 
                      or(!('type' in el)
                         , ('type' in el) && isEscapableType(el.type) && !el.readOnly)
                      , isContentEditable(el))
        }
        var isCtrlR = function(e, keycode){
            return e.ctrlKey && KEYCODE.R === keycode
        }
        var isArray = function(x){
            return /Array/.test(Object.prototype.toString.call(x))
        }
        
        var getEvt = function(e){
            return e || window.event
        }
        var getTarget = function(e){
            return e.target || e.srcElement
        }
        var getKeycode = function(e){
            return e.keyCode || e.which
        }
        var preventDefault = function(e){
            e.preventDefault && e.preventDefault()
            e.returnValue = false
            return false
        }
        var listen = function(listen){
            return function(evtNames, handler){
                if (!isArray(evtNames)){
                    evtNames = [evtName]
                }
                var i = 0
                  , len = evtNames.length
                for (; i < len; ++i){
                    listen(evtNames[i], handler)
                }
            }
        }(function(evtName, handler){
            if (or(document['addEventListener'] && (document['addEventListener'].apply(document, arguments) || true)
                   , document['attachEvent'] && (document['attachEvent'].apply(document, arguments) || true))){
                document['on'+evtName] = handler
            }
            
        })
        
        var or = function(){
            var ret = false
              , i = 0
              , len = arguments.length
            for (; !ret && i < len; ++i){
                ret = ret || arguments[i]
            }
            return ret
        }
        var handler = function(e){
                        if (!started) return true
            var evt = getEvt(e)
              , el = getTarget(evt)
              , keyCode = getKeycode(evt)

            if (or(KEYCODE.BACKSPACE === keyCode && !isEscapableBackspace(el)
                  , isCtrlR(evt, keyCode))){
                return preventDefault(evt)
            }
        }
        
        listen(['keydown'], handler)
    }(window.nobsgb = {}))

代碼時間.cljs

core.cljs

(ns nobsgb.core
  (:require [nobsgb.dom :as dom]
            [nobsgb.pred :as pred]))

(def started false)
(defn ^:export start []
  (set! started true))
(defn ^:export stop []
  (set! started false))

(defn handler
  "keydown事件響應函數"
  [e]
  (when started
    (let [evt (dom/get-evt e)
          el (dom/get-el evt)
          key-code (dom/get-key-code evt)
          ctrl-key (dom/get-ctrl-key evt)
          read-only (dom/get-read-only el)
          type (dom/get-type el)
          content-editable (dom/get-content-editable el)
          tag (dom/get-tag el)]
      (if-not
        (pred/escapable?
          key-code read-only type tag content-editable ctrl-key)
        (dom/prevent-default evt)
        true))))

(defonce init
  (#(dom/listen! js/document "keydown" handler)))

dom.cljs

(ns nobsgb.dom)

(defn get-evt
  [e]
  (if (some? e) e (.event js/window)))

(defn get-el
  [e]
  (let [el (.-target e)]
    (if (some? el) el (.-srcElement e))))

(defn get-key-code
  [e]
  (.-keyCode e))

(defn get-ctrl-key
  [e]
  (.-ctrlKey e))

(defn get-read-only
  [el]
  (-> el (aget "readOnly") js/Boolean))

(defn get-type
  [el]
  (let [type (.-type el)]
    (if (some? tpye) type "")))

(defn get-tag
  [el]
  (.-tagName el))

(defn get-content-editable
  [el]
  (.-isContentEditable el))

(defn prevent-default
  [e]
  (if (some? (.-preventDefault e))
    (do
      (.preventDefault e)
      (set! (.-returnValue e) false)
      false)
    true))

(defn listen!
  [el evt-name handler]
  (cond
    (fn? (.-addEventListener el)) (.addEventListener el evt-name handler)
    (fn? (.-attachEvent el))      (.attachEvent el (str "on" evt-name) handler)
    :else (aset el (str "on" evt-name) handler)))

pred.cljs

(ns nobsgb.pred)
;;;; 斷言

(defonce ^:const KEYCODES
  {:backspace 8
   :r 82})

(defn matches-key?
  "是否匹配指定鍵碼"
  [indicated-key-code key-code]
  (= indicated-key-code key-code))

(def ^{:doc "是否爲退格鍵"}
  backspace?
  (partial matches-key? (:backspace KEYCODES)))

(def ^{:doc "是否爲字母R鍵"}
  r?
  (partial matches-key? (:r KEYCODES)))

(defn with-ctrl?
  "是否在按ctrl的基礎上按其餘鍵"
  [ctrl-key]
  (or (= ctrl-key "1")
      (true? ctrl-key)))

(defn ctrl+r?
  "是否爲ctrl+r"
  [ctrl-key key-code]
  (and (with-ctrl? ctrl-key)
       (r? key-code)))
(def not-ctrl+r? (complement ctrl+r?))

(defn escapable-type?
  "是否爲可跳過的type屬性"
  [type]
  (some?
    (some->> type
      (re-matches #"(?i)text|password|tel|number|email|search|url"))))

(defn escapable-tag?
  "是否爲可跳過的tag"
  [tag]
  (some?
    (some->> tag
      (re-matches #"(?i)input|textarea"))))

(def ^{:doc "是否設置爲可編輯元素"}
  content-editable? identity)

(def ^{:doc "是否設置爲只讀"}
  read-only? identity)
(def writable? (complement read-only?))

(defn escapable-backspace?
  [key-code read-only type tag content-editable]
  (and (backspace? key-code)
       (writable? read-only)
       (or (escapable-type? type)
           (escapable-tag? tag)
           (content-editable? content-editable))))

(defn escapable?
  [key-code read-only type tag content-editable ctrl-key]
  (or
    (and (not-ctrl+r? ctrl-key key-code)
         (not (backspace? key-code)))
    (escapable-backspace? key-code read-only type tag content-editable)))

總結

尊重原創，轉載請註明來自：http://www.cnblogs.com/fsjohn... ^_^肥仔John

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