动手写个数字输入框2：起手式——拦截非法字符-阿里云开发者社区

前言

最近在用Polymer封装纯数字的输入框，开发过程中发现不是坑，也有不少值得研究的地方。本系列打算分4篇来叙述这段可歌可泣的踩坑经历：

从源头抓起——拦截非法字符

从《动手写个数字输入框1：input[type=number]的遗憾》中我们了解到input[type=number]基本不能满足我们的需求，为了简单化我们就直接在input[type=text]上加工出自己的数字输入框吧。
首先很明确的一点是最终数值可以包含以下字符[+-0-9.]，而可输入的功能键为Backspace,Delete,Arrow-Left,Arrow-Right,Arrow-Up,Arrow-Down和Tab。
于是我们可以设置如下规则了

// 断言库
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()
    }
})

扩大非法字符集

还记得min,max,precision吗？

当min大于等于0时，负号应该被纳入非法字符；
当max小于0时，正号应该被纳入非法字符；
当precision为0时，小数点应该被纳入非法字符。于是我们添加如下规则，并修改一下isValid就好了

// 获取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)))

预判断

到这里为止我们已经成功地拦截了各种非法字符，也就是最终值必须之含[+-0-9.]，但含这些字符跟整体符合数值格式就是两回事了。因此我们要继续补充下面两步，并且由于keydown事件触发时value值还没被修改，于是我们需要将value值和当前输入值做组合来做预判，进一步扩大非法字符集。

通过正则检查最终值是否符合格式要求(是否存在多个小数点也会在这一步处理掉);
检查最终值是否在min和max范围内。

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
    // 拦截非法字符
    if (isValid(e)){
        prevented = false

        // 预判断
        if (anyPass(comp(anyPass(isMinus, isDigit, isDot), keyCode), isPlus)(e)){
            var str = view(lensTargetValue)(e) + prop('key')(e)
            // 预判断格式
            prevented = !isValidStr(view(lensTargetPrecision)(e))(str)

            // 预判断值范围
            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()
    }
})

附录：工具函数

// 工具函数，请无视我吧: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)

总结

现在可以终于可以牢牢控制住用户输入了，直到用户切换到IME为止:-<当使用IME输入时会发现上述措施一点用也没有，不用皱眉了，后面我们会一起把IME KO掉！
尊重原创，转载请注明来自：http://www.cnblogs.com/fsjohnhuang/p/6929167.html ^_^肥仔John

如果您觉得本文的内容有趣就扫一下吧！捐赠互勉！