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Maps

TypeScript (obviously) also has a built-in for maps, which are collections of key-value pairs. You can specify the types of the keys and values using type parameters <K, V>.

// A Map with string keys and number values
const podracerSpeeds = new Map<string, number>();

podracerSpeeds.set("Anakin Skywalker", 947);
podracerSpeeds.set("Sebulba", 941);

podracerSpeeds.set("R2-D2", true);
// Error: Argument of type 'true' is not assignable to parameter of type 'number'

podracerSpeeds.set(420, 69);
// Error: Argument of type 'number' is not assignable to parameter of type 'string'

A map is a "set-like" object, and as such uses the size property instead of length.

console.log(podracerSpeeds.size);
// 2

How to easily iterate over a map:

for (const [racer, speed] of podracerSpeeds) {
  console.log(`${racer} raced at ${speed} speed`);
}
// Anakin raced at 947 speed
// Sebulba raced at 941 speed

Here's the most important methods of a map, get, delete, and has.

console.log(podracerSpeeds.get("Sebulba"));
// 941

console.log(podracerSpeeds.has("Sebulba"));
// true

podracerSpeeds.delete("Sebulba");
console.log(podracerSpeeds.get("Sebulba"));
// undefined

Assignment

Let's add file sharing to Support.ai's internal email system.

Complete the getFileLength function. It takes:

A Map<string, string> that represents filenames -> fileContents
A specific filename to get the length of

It returns the number of bytes in the file's contents. If the filename is not present in the map, return 0.

Use the TextEncoder class and its encode method to encode the file contents (a string) into a Uint8Array, and return the length of the resulting array.