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HTML

Controlled array to restrict length

Babel + JSX

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
  
});