Как обратится к массиву в динамической функции

var materials = [ 
  {width: 10}, {width: 20}, {width: 30} 
] 
 
function getFromTable(i, arr, prop) { 
  if (!Array.isArray(arr)) throw "second arg must be arr"; 
  if (!arr[i]) throw "no index in arr"; 
  if (!arr[i][prop]) throw "no prop in index arr";; 
  return arr[i][prop]; 
} 
 
console.log(getFromTable(2, materials, 'width'));

var materials = [{width: 10}, {width: 20}] 
 
function getFromTable(i, arr, property) { 
  var execCmd = arr + '[' + i + ']' + '["' + property + '"]'; 
  return eval(execCmd); 
} 
 
console.log(getFromTable(1, 'materials', 'width'));

'use strict'; 
 
var tabels = { 
	tab1 : [ 
	{prop1 : "p1", 
	 prop12 : "p12"}, 
	{prop2 : "p2"}, 
	{prop3 : "p3"} 
	], 
		tab2 : [ 
	{prop1 : "p1"}, 
	{prop2 : "p2"}, 
	{prop3 : "p3"} 
	] 
}; 
    
function getFromTable(index, arr, property){ 
	return tabels[arr][index][property]; 
}; 
    
console.log(getFromTable(0,'tab1','prop12'));