To Arrow Function or not to Arrow Function

MyClass.js

var MyClass = (function () {
    function MyClass() {
    }
    MyClass.prototype.add = function (a, b) {
        return a + b;
    };
    MyClass.prototype.partialAdd = function (a) {
        var _this = this;
        return function (b) {
            return _this.add(a, b);
        }
    };
    MyClass.prototype.partialAdd2 = function (a) {
        return function (b) {
            return this.add(a, b);
        }
    };
    return MyClass;
})();

MyClass.ts

class MyClass {
    constructor() {
    }

    private add(a, b) {
        return a + b;
    }

    public partialAdd(a) {
        return (b) => {
            return this.add(a, b);
        }
    }

    public partialAdd2(a) {
        return function(b) {
            return this.add(a, b);
        }
    }
}

MyClass2.ts

class MyClass {
    constructor() {
    }

    private add(a, b) {
        return a + b;
    }

    public partialAdd(a) {
        var that = this;
        return function(b) {
            // this is accessible inside the function
            // and points to the object to which the function was applied
            var _this = this;
            // that is accessible inside the function through the closure
            // and points to the object that had partialAdd called
            return that.add(a, b);
        }
    }
}