Using an integer as a key in an associative array in JavaScript

Question

When I create a new JavaScript array, and use an integer as a key, each element of that array up to the integer is created as undefined.

For example:

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Answer 1

If the use case is storing data in a collection then ECMAScript 6 provides the Map type.

It's only heavier to initialize.

Here is an example:

const map = new Map();
map.set(1, "One");
map.set(2, "Two");
map.set(3, "Three");

console.log("=== With Map ===");

for (const [key, value] of map) {
    console.log(`${key}: ${value} (${typeof(key)})`);
}

console.log("=== With Object ===");

const fakeMap = {
    1: "One",
    2: "Two",
    3: "Three"
};

for (const key in fakeMap) {
    console.log(`${key}: ${fakeMap[key]} (${typeof(key)})`);
}

Result:

=== With Map ===
1: One (number)
2: Two (number)
3: Three (number)
=== With Object ===
1: One (string)
2: Two (string)
3: Three (string)