This tutorial will teach the Map data structure in TypeScript with Examples.
TypeScript Map allows you to store key-value pairs, similar to the maps in other programming languages e.g. Java HashMap.TypeScript Map Basic Usage
// Create a new Map
const myMap = new Map();
// Set values
myMap.set("key1", "value1");
myMap.set("key2", "value2");
// Get values
console.log(myMap.get("key1")); // Output: "value1"
console.log(myMap.get("key2")); // Output: "value2"
// Check if a key exists
console.log(myMap.has("key1")); // Output: true
// Get the number of key-value pairs
console.log(myMap.size); // Output: 2
// Delete a key-value pair
myMap.delete("key2");
// Check if a key exists (after deletion)
console.log(myMap.has("key2")); // Output: false
// Clear the Map
myMap.clear();
// Check the size of the Map (after clearing)
console.log(myMap.size); // Output: 0
Output:
"value1"
"value2"
true
2
false
0
- myMap.set(key, value) – adds a new entry in the Map.
- myMap.get(key) – retrieves the value for a given key from the Map.
- myMap.has(key) – checks if a key is present in the Map. Returns true or false.
- myMap.size – returns the count of entries in the Map.
- myMap.delete(key) – deletes a key-value pair using its key. If the key is found and deleted, it returns true, else returns false.
- myMap.clear() – deletes all entries from the Map.
Iterating over Map
const myMap = new Map();
myMap.set("key1", "value1");
myMap.set("key2", "value2");
myMap.set("key3", "value3");
// Iterate over keys
for (const key of myMap.keys()) {
console.log(key);
}
// Output:
// "key1"
// "key2"
// "key3"
// Iterate over values
for (const value of myMap.values()) {
console.log(value);
}
// Output:
// "value1"
// "value2"
// "value3"
// Iterate over entries (key-value pairs)
for (const [key, value] of myMap.entries()) {
console.log(key, value);
}
// Output:
// "key1" "value1"
// "key2" "value2"
// "key3" "value3"
Iterating over keys:
for (const key of myMap.keys()) {
console.log(key);
}
This loop iterates over the map's keys using the keys() method. The loop body logs each key to the console. In this case, it will output:
"key1"
"key2"
"key3"
Iterating over values:
for (const value of myMap.values()) {
console.log(value);
}
This loop iterates over the values of the map using the values() method. The loop body logs each value to the console. The output will be:
"value1"
"value2"
"value"
Iterating over entries (key-value pairs):
for (const [key, value] of myMap.entries()) {
console.log(key, value);
}
This loop iterates over the entries (key-value pairs) of the map using the entries() method. The loop body logs each key-value pair to the console. The output will be:
"key1" "value1"
"key2" "value2"
"key3" "value"
Using Objects as Keys
const myMap = new Map();
const key1 = { id: 1 };
const key2 = { id: 2 };
myMap.set(key1, "value1");
myMap.set(key2, "value2");
console.log(myMap.get(key1)); // Output: "value1"
console.log(myMap.get(key2)); // Output: "value2"
In this above example, objects are used as keys. The Map uses strict equality (===) to compare keys, so two objects with the same properties/values are considered different keys. This allows you to use objects as keys and retrieve their corresponding values from the Map.
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