Get field type in Typescript

Question

I have class in Typescript. It has some fields

field1 : ko.observable<number>();
field2 : ko.observable<string>('');
...

In some function in another class I've tried to loop through every object field and for fields of type number I need to perform some modifications.

How can I detect this?

---

I've tried next, but always get type as string which is logically. locationModel filled with values from HTML form, where inputs is of type text

 Object.keys(locationModel)
 .forEach(property => {
                if (typeof locationModel[property]() === 'number') { }
                else{ }
            }
        });

Answer 1

If you want to put automatic type conversion into knockout you can create an extender for that.

In its most basic form it could return a writable computed that either:

• converts the incoming value on write and stores the converted value in the observable, or
• stores the incoming value in the observable unchanged and converts it on read.

An implementation of the latter could like this – run the snippet below and note how the type reflects in the viewmodel:

ko.extenders.type = function (target, type) {
    var typedValue = ko.pureComputed({
        read: function () {
            var value = target();
            if (typeof value === "undefined" || value === null) {
                return value;
            } else {
                return type(value);
            }
        },
        write: target
    });
    typedValue.raw = target;
    return typedValue;
};

var vm = {
    num: ko.observable().extend({type: Number}),
    str: ko.observable().extend({type: String})
};

ko.applyBindings(vm);

// init some values
vm.num(100);
vm.str(100);

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/3.2.0/knockout-min.js"></script>

Num: <input data-bind="value: num"> (raw: <span data-bind="text: num.raw"></span>)<br>
Str: <input data-bind="value: str"> (raw: <span data-bind="text: str.raw"></span>)<br><br>

<hr>
View Model:<br>
<pre data-bind="text: ko.toJSON($root, null, 2)"></pre>