读在淘汰赛可计算并不总是与扩展

Question

发射，这可能是最简单的用小提琴http://jsfiddle.net/LkqTU/32190/

来形容我有那么它舍入到两位数字，不允许非数字它有一个扩展可观察到的所谓的价格。

我有一个可写的计算可观察性，在它前面放一个美元符号。

但是，如果扩展器返回0.第二次发生$ 0不会返回到文本框（计算的可观察值），所以如果我在文本框中输入hello world（computed observable），价格正确报告0和格式化的价格显示$ 0。但是，如果我将其清除并再次输入hello world。这次价格仍然是0美元，但格式化的价格文本框显示你好世界（即使格式化的价格报告$ 0）。必须在某处丢失通知？

这里是代码。

ko.extenders.numeric = function(target, precision) { 
    //create a writable computed observable to intercept writes to our observable 
    var result = ko.pureComputed({ 
    read: target, //always return the original observables value 
    write: function(newValue) { 
     var current = target(), 
     roundingMultiplier = Math.pow(10, precision), 
     newValueAsNum = isNaN(newValue) ? 0 : parseFloat(+newValue), 
     valueToWrite = Math.round(newValueAsNum * roundingMultiplier)/roundingMultiplier; 

     //only write if it changed 
     if (valueToWrite !== current) { 
     target(valueToWrite); 
     } else { 
     //if the rounded value is the same, but a different value was written, force a notification for the current field 
     if (newValue !== current) { 
      target.notifySubscribers(valueToWrite); 
     } 
     } 
    } 
    }).extend({ 
    notify: 'always' 
    }); 

    //initialize with current value to make sure it is rounded appropriately 
    result(target()); 

    //return the new computed observable 
    return result; 
}; 


function model() { 
    var self = this; 

    this.price = ko.observable('29.01').extend({ 
    numeric: '2' 
    }); 
    this.formattedPrice = ko.computed({ 
    read: function() { 
     return '$' + this.price() 
    }, 
    write: function(value) { 
     value = parseFloat(value.replace(/[^\.\d]/g, "")); 
     this.price(isNaN(value) ? 0 : value); 
    }, 
    owner: this 
    }); 
} 

var mymodel = new model(); 

$(document).ready(function() { 
    ko.applyBindings(mymodel); 

}); 

Answer 1

什么似乎为我被延长formattedPrice计算的变量总是通知和修改写入方法，只是在价值传递，而不是检查isNaN工作;您的扩展做到这一点无论如何，迫使一0时，使您的if (newValue !== current)测试永远不会返回为NEWVALUE真实和电流将始终处于这种情况下0（NAN == 0 将通过检查！）：

this.formattedPrice = ko.computed({ 
    read: function() { 
     return '$' + this.price() 
    }, 
    write: function(value) { 
     value = parseFloat(value.replace(/[^\.\d]/g, "")); 
     this.price(value); //just pass in nan or the value so the extender can check/notify if newValue !== current 
    }, 
    owner: this 
    }).extend({ 
    notify: 'always' 
    }); 

更新提琴：http://jsfiddle.net/LkqTU/32192/