Clever Geek Handbook

KnockoutObservable <number> returns string when bound to typescript input

I am using knockout version 3.2.0 and its definitelyTyped definitions from nuget:

I have an input bound property (type number) with value binding, property definition:

export class SomeClass {
    myProp: KnockoutObservable<number>;

   constructor() {
       myProp = ko.observable(0);
   }
}

Now, messing around with the console, when the class is initialized, the property returns 0 when called. However, after changing the input value, the property starts returning a string, eg. if I change it to 2, the return value is "2". This is obviously a problem when combining two such properties.

var x = myinstance.myProp() + myinstance.myProp();

The result is not 4, as you would expect, the result is "22", concatenation.

Is there a sane solution? Is this a knockout bug or documented behavior?

+3


source share


1 answer


You have bound a string value to a numeric type and are expecting automatic type conversion during binding. This won't work because, in the first place, KnockoutJS is a Javascript framework that doesn't know anything about the Typescript Type System.



You can either make the property a writable observable, or you can enter a read-only counter that simply triggers the current value of "myProp" via parseInt ().

+3


source






More articles:


All Articles