What is a Map in TypeScript?
In TypeScript, a Map is a built-in data structure that allows you to store and retrieve key-value pairs. It is similar to an object in JavaScript, but with a few key differences. A Map can use any value as the key, not just strings or symbols, and it maintains the order in which keys were added.
Creating a Map in TypeScript
To create a Map in TypeScript, you can use the Map constructor function. You can pass an array of key-value pairs to the constructor, or you can add entries to the Map using the set() method. Here’s an example: “` const myMap = new Map([ [‘key1’, ‘value1’], [‘key2’, ‘value2’] ]); myMap.set(‘key3’, ‘value3’); “`
Retrieving Values from a TypeScript Map
To retrieve a value from a TypeScript Map, you can use the get() method. If the key is not found in the Map, get() will return undefined. Here’s an example: “` const myMap = new Map([ [‘key1’, ‘value1’], [‘key2’, ‘value2’] ]); const value1 = myMap.get(‘key1’); // returns ‘value1’ const value3 = myMap.get(‘key3’); // returns undefined “`
Iterating over a TypeScript Map
To iterate over the entries in a TypeScript Map, you can use the entries() method. This method returns an iterator that yields an array of [key, value] pairs for each entry in the Map. Here’s an example: “` const myMap = new Map([ [‘key1’, ‘value1’], [‘key2’, ‘value2’] ]); for (const [key, value] of myMap.entries()) { console.log(`${key}: ${value}`); } “`
Checking if a Key Exists in a TypeScript Map
To check if a key exists in a TypeScript Map, you can use the has() method. This method returns true if the key is found in the Map, and false otherwise. Here’s an example: “` const myMap = new Map([ [‘key1’, ‘value1’], [‘key2’, ‘value2’] ]); const hasKey1 = myMap.has(‘key1’); // returns true const hasKey3 = myMap.has(‘key3’); // returns false “`
Deleting Entries from a TypeScript Map
To delete an entry from a TypeScript Map, you can use the delete() method. This method removes the entry with the specified key from the Map. Here’s an example: “` const myMap = new Map([ [‘key1’, ‘value1’], [‘key2’, ‘value2’] ]); myMap.delete(‘key1’); “`
Using Objects as Keys in a TypeScript Map
In TypeScript, you can use any value as the key in a Map, including objects. When using objects as keys, however, you need to be aware of how equality is determined. By default, two objects are only equal if they are the same object in memory. Here’s an example: “` const myMap = new Map(); const obj1 = { id: 1 }; const obj2 = { id: 1 }; myMap.set(obj1, ‘value1’); console.log(myMap.get(obj1)); // returns ‘value1’ console.log(myMap.get(obj2)); // returns undefined “`
Conclusion
In conclusion, TypeScript Maps are a powerful tool for storing and retrieving key-value pairs in your code. They offer several advantages over plain JavaScript objects, including support for any value as a key and maintaining the order of entries. By understanding how to create, retrieve, iterate over, and delete entries from a Map, you can take advantage of this feature in your TypeScript projects.