whole_func_string: function updateArrayItem(observer, idx, value) {
      observer.set(idx, value);
      this[idx] = value;
  }
func_code_string: function updateArrayItem(observer, idx, value) {
      observer.set(idx, value);
      this[idx] = value;
  }
func_documentation_string: Update array item value
  
  @param {Observer} observer the observer
  @param {number} idx the index to update
  @param {*} value the value to set