Closure for true private field in JavaScript using TypeScript

Question

I am trying to rewrite one of my useful JavaScript class with TypeScript. In my JavaScript class I use closure variable self for implementing private field. It is useful in event handlers, for example onkeypress, where important to know invoker of event and current instance of my class.

var MyClass = function (valueHolder) {
            var self = this;
            this.valueHolder = valueHolder;

            MyClass.prototype.DoUsefullactions = function (value) {
                alert(value);
            }

            MyClass.prototype.onclickForHolder = function (e) {
                var value = $(this).val(); //value from attached input
                self.DoUsefullactions(value);
            }

            MyClass.prototype.GetSelf = function () {
                return self;
            }

            this.valueHolder.onclick = this.onclickForHolder;
        }

I can't find how to make what closure variable what will be available for all methods of the class without this.self syntax in TypeScript and make true private members in JavaScript way.

Assigning properties to prototype in constructor function is not good. It'll assign this on every constructor call. — Shiplu Mokaddim
– Shiplu Mokaddim, Commented Oct 17, 2012 at 12:19

izb · Accepted Answer · 2012-10-17 13:06:39Z

3

There's an alternative function syntax for this. Simply use:

MyClass.prototype.onclickForHolder = e => {
    var value = $(e.target).val(); //value from attached input
    this.DoUsefullactions(value);
}

this will refer to the outer this and TypeScript will add a self-type variable behind the scenes.

answered Oct 17, 2012 at 13:06

izb

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1 Comment

Menotaurus Over a year ago

thank you, i know this version for solving problem, i'am assuming abstract solution exists in this situation in TypeScript

Eduardo Ortiz · Accepted Answer · 2012-10-26 16:36:18Z

1

try

 MyClass.prototype.onclickForHolder =(ev:Event) =>this.DoUsefullactions(this,ev);

answered Oct 26, 2012 at 16:36

Eduardo Ortiz

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1 Comment

Axel Isouard Over a year ago

It would be appreciated if you explain why he should try that.

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