Arrays vs Objects

Arrays and objects are two of the main data structures in JavaScript. In the following table they are compared side by side:

Arrays Objects
Store values Store key-value pairs
Access by index Access by key
Constructors

var arr = []; // preferred
new Array();
Constructors

var obj = {};
new Stack(); // or other data type
Access

// access by index

arr[13]; // use bracket notation

var tmp = 13; // tmp stores index
var arr[tmp]; // retrieve value
Access

// access by key

obj.key; // use dot notation
obj["key"]; // use bracket notation

var tmp = "key"; // tmp stores key
obj[tmp]; // retrieve value
Loop

var arr = [1, 2, 3];
for (var i = 0; i < arr.length; i++) {
  var value = arr[i];
  console.log(value);
}
Loop

var obj = { a: 1, b: 2, c: 3 };
for (var key in obj) {
  var value = obj[key];
  console.log(key + " " + value);
}

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