摘要：前言最近在用封裝純數(shù)字的輸入框，開發(fā)過程中發(fā)現(xiàn)不是坑，也有不少值得研究的地方。因此我們要繼續(xù)補(bǔ)充下面兩步，并且由于事件觸發(fā)時(shí)值還沒被修改，于是我們需要將值和當(dāng)前輸入值做組合來做預(yù)判，進(jìn)一步擴(kuò)大非法字符集。

?最近在用Polymer封裝純數(shù)字的輸入框，開發(fā)過程中發(fā)現(xiàn)不是坑，也有不少值得研究的地方。本系列打算分4篇來敘述這段可歌可泣的踩坑經(jīng)歷：

《動(dòng)手寫個(gè)數(shù)字輸入框1：input[type=number]的遺憾》

《動(dòng)手寫個(gè)數(shù)字輸入框2：起手式——攔截非法字符》

《動(dòng)手寫個(gè)數(shù)字輸入框3：痛點(diǎn)——輸入法是個(gè)魔鬼》

《動(dòng)手寫個(gè)數(shù)字輸入框4：魔鬼在細(xì)節(jié)——打磨光標(biāo)位置》

?從《動(dòng)手寫個(gè)數(shù)字輸入框1：input[type=number]的遺憾》中我們了解到input[type=number]基本不能滿足我們的需求，為了簡(jiǎn)單化我們就直接在input[type=text]上加工出自己的數(shù)字輸入框吧。
?首先很明確的一點(diǎn)是最終數(shù)值可以包含以下字符[+-0-9.]，而可輸入的功能鍵為Backspace,Delete,Arrow-Left,Arrow-Right,Arrow-Up,Arrow-Down和Tab。
于是我們可以設(shè)置如下規(guī)則了

// 斷言庫
const keyCode = anyPass(prop("keyCode"), prop("which"))
const isBackspace = eq(8)
        , isDelete = eq(46)
        , isArrowLeft = eq(37)
        , isArrowRight = eq(38)
        , isArrowUp = eq(39)
        , isArrowDown = eq(40)
        , isTab = eq(9)
        , isMinus = anyPass(eq(109), eq(189))
        , isDot = anyPass(eq(110), eq(190))
        , isDigit = anyPass(
                                    allPass(lte(49), gte(57))
                                    , allPass(lte(96), gte(105)))
        , isPlus = anyPass(
                                comp(eq(107), keyCode)
                                , allPass(
                                        prop("shiftKey")
                                        , comp(eq(187), keyCode)))

const isValid  = anyPass(
                                    comp(
                                        anyPass(isBackspace, isDelete, isArrowLeft
                                            , isArrowLeft, isArrowUp, isArrowDown
                                            , isTab, isMinus, isDot, isDigit)
                                        , keyCode)
                                    , isPlus)

$("input[type=text]").addEventListener("keydown", e => {
    if (!isValid(e)){
        e.preventDefault()
    }
})

?還記得min,max,precision嗎？

當(dāng)min大于等于0時(shí)，負(fù)號(hào)應(yīng)該被納入非法字符；

當(dāng)max小于0時(shí)，正號(hào)應(yīng)該被納入非法字符；

當(dāng)precision為0時(shí)，小數(shù)點(diǎn)應(yīng)該被納入非法字符。于是我們添加如下規(guī)則，并修改一下isValid就好了

// 獲取min,max,precision值
const lensTarget = lens(a => a.target || a.srcElement)
        , lensMin = lens(a => Number(a.min) || Number(attr(a, "min")) || Number.MIN_SAFE_INTEGER)
        , lensMax = lens(a => Number(a.max) || Number(attr(a, "max")) || Number.MAX_SAFE_INTEGER)
        , lensPrecision = lens(a => Number(a.precision) || Number(attr(a, "precision")) || 0)
        , lensValue = lens(a => a.value)

const lensTargetMin = lcomp(lensTarget, lensMin)
        , lensTargetMax = lcomp(lensTarget, lensMax)
        , lensTargetPrecision = lcomp(lensTarget, lensPrecision)

const isValid  = anyPass(
                                    comp(
                                        anyPass(isBackspace, isDelete, isArrowLeft
                                            , isArrowLeft, isArrowUp, isArrowDown
                                            , isTab, isDigit)
                                        , keyCode)
                                    , allPass(
                                            comp(gt(0), view(lensTargetMin))
                                            , comp(isMinus, keyCode))
                                    , allPass(
                                            comp(lte(0), view(lensTargetMax))
                                            , isPlus)
                                    , allPass(
                                            comp(lt(0), view(lensTargetPrecision))
                                            , comp(isDot, keyCode)))

?到這里為止我們已經(jīng)成功地?cái)r截了各種非法字符，也就是最終值必須之含[+-0-9.]，但含這些字符跟整體符合數(shù)值格式就是兩回事了。因此我們要繼續(xù)補(bǔ)充下面兩步，并且由于keydown事件觸發(fā)時(shí)value值還沒被修改，于是我們需要將value值和當(dāng)前輸入值做組合來做預(yù)判，進(jìn)一步擴(kuò)大非法字符集。

通過正則檢查最終值是否符合格式要求(是否存在多個(gè)小數(shù)點(diǎn)也會(huì)在這一步處理掉);

檢查最終值是否在min和max范圍內(nèi)。

const isValidStr = precision =>
                                     a => RegExp("^[+-]?[0-9]*"+ (precision ? "(.[0-9]{0," + precision + "})?" : "") + "$").test(a)
const lensValue = lens(a => a.value)
      , lensTargetValue = lcomp(lensTarget, lensValue)

$("input[type=text]").addEventListener("keydown", e => {
    var prevented = true
    // 攔截非法字符
    if (isValid(e)){
        prevented = false

        // 預(yù)判斷
        if (anyPass(comp(anyPass(isMinus, isDigit, isDot), keyCode), isPlus)(e)){
            var str = view(lensTargetValue)(e) + prop("key")(e)
            // 預(yù)判斷格式
            prevented = !isValidStr(view(lensTargetPrecision)(e))(str)

            // 預(yù)判斷值范圍
            if (!prevented){
                if (str == "-") str = "-0"
                if (str == "+") str = "0"
                if (str == ".") str = "0"

                prevented = !allPass(
                                            gte(view(lensTargetMax)(e))
                                            , lte(view(lensTargetMin)(e)))(Number(str))
            }
        }
    }

    if (prevented){
        e.preventDefault()
    }
})

// 工具函數(shù)，請(qǐng)無視我吧:D
const comp =
             (...fns) =>
             (...args) => {
                 let len = fns.length
                 while (len--){
                     args = [fns[len].apply(null, args)]
                 }
                 return args.length > 1 ? args : args[0]
             }
const isSome = x => "undefined" !== typeof x && x !== null
const invokerImpl =
                n =>
                o =>
                m =>
                (...args) => {
                    let args4m = args.splice(0, n)
                        , times = Number(args[0]) || 1
                        , ret = []
                    while (times--){
                        var tmpRet
                        try{
                            tmpRet = o[m].apply(o, args4m)
                        }
                        catch(e){
                            tmpRet = void 0
                        }
                        ret.push(tmpRet)
                    }
                    return ret.length > 1 ? ret : ret[0]
                }
const curry2Partial =
        fn =>
        (...args) => {
                let c = true
                        , i = 0
                        , l = args.length
                        , f = fn
                for (;c && i < l; ++i){
                        c = isSome(args[i])
                        if (c){
                                f = f(args[i])
                        }
                }
                return f
        }
const invoker = curry2Partial(invokerImpl)
const and = (...args) => args.reduce((accu, x) => accu && x, true)
const or = (...args) => args.reduce((accu, x) => accu || x, false)
const allPass = (...fns) => v => fns.reduce((accu, x) => accu && x(v), true)
const anyPass = (...fns) => v => fns.reduce((accu, x) => accu || x(v), false)
const eq = a => b => a === b
const gt = a => b => a > b
const gte = a => anyPass(eq(a), gt(a))
const lt = a => b => a < b
const lte = a => anyPass(eq(a), lt(a))
const prop = k => o => o[k]
const lens = (g, s) => ({getter: g, setter: s})
const lensPath = (...args) => ({ getter: a => args.reduce((accu, x) => accu && accu[x], a) })
const lcomp = (...lenses) => ({ getter: a => lenses.reduce((accu, lens) => accu && lens.getter(accu), a)})
const view = l => a => l.getter(a)

const $ = invoker(1, document, "querySelector")
const attr = (o, a) => invoker(1, o, "getAttribute")(a)

?現(xiàn)在可以終于可以牢牢控制住用戶輸入了，直到用戶切換到IME為止:-<當(dāng)使用IME輸入時(shí)會(huì)發(fā)現(xiàn)上述措施一點(diǎn)用也沒有，不用皺眉了，后面我們會(huì)一起把IME KO掉！
尊重原創(chuàng)，轉(zhuǎn)載請(qǐng)注明來自：http://www.cnblogs.com/fsjohn... ^_^肥仔John