Why can I add named properties to an array as if it were an object?

Question

The following two different code snippets seem equivalent to me:

var myArray = Array();
myArray[\'A\'] = \"Athens\";
myArray[\'B\'] = \"Berlin\";
         


        

Answer 1

You can add named properties to almost anything in javascript but that doesn't mean that you should. Array in javascript should be used as a list, if you want an associative array use Object instead.

Beware that if you really want to use an Array with named properties instead of Object those properties won't be accessible in a for...of loop and you might also get unexpected results when JSON encoding it to pass it around. See example below where all non-numeric indexes get ignored:

let arr = [];
let obj = {};

arr['name'] = 'John';
obj['name'] = 'John';

console.log(arr);    // will output [name: "John"]
console.log(obj);    // will output {name: "John"}

JSON.stringify(arr); // will return [] <- not what you expected
JSON.stringify(obj); // will return {"name":"John"}