TypeScript: how to declare array of fixed size for type checking at Compile Time

Question

Update: These checks are meant for compile time, not at runtime. In my example, the failed cases are all caught at compile

Answer 1

Here is a simple example of a class to control the length of its internal array. It isn't fool-proof (when getting/setting you may want to consider whether you are shallow/deep cloning etc:

https://jsfiddle.net/904d9jhc/

class ControlledArray {

  constructor(num) {
    this.a = Array(num).fill(0); // Creates new array and fills it with zeros
  }

  set(arr) {
    if (!(arr instanceof Array) || arr.length != this.a.length) {
      return false;
    }
    this.a = arr.slice();
    return true;
  }

  get() {
    return this.a.slice();
  }

}

$( document ).ready(function($) {

  var m = new ControlledArray(3);

  alert(m.set('vera')); // fail
  alert(m.set(['vera', 'chuck', 'dave'])); // pass

  alert(m.get()); // gets copy of controlled array

});