Angular ForEach in Typescript

Question

I see many answers about using ngFor when I search for this, but I understand ngFor. I'm asking about the angular.forEach() constructor used in my Angular 1 controllers. These are flagged as errors in TS and do not compile.

For example, I have one with a nested loop:

 _this.selectChildren = function (data, $event) {
  var parentChecked = data.checked;
  angular.forEach(_this.hierarchicalData, function (value, key) {
    angular.forEach(value.children, function (value, key) {
      value.checked = parentChecked;
    });
  });
};

What does this construct look like in Typescript for Angular 4?