How to Iterate Over Entries (Key-Value Pairs) in a Map in JavaScript

How to Iterate Over Entries (Key-Value Pairs) in a Map in JavaScript ?

Answer

To iterate over entries (key-value pairs) in a map in JavaScript, you can use the entries method along with a for...of loop or the forEach method. This allows you to access each key-value pair in the map.

✐ Examples

1 Iterating Over Entries Using for...of Loop

We can iterate over entries in a map in JavaScript using a for...of loop with the entries method, which provides a convenient syntax for iterating over all key-value pairs in the map.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the entries method to get an iterable of the key-value pairs in the map.
We iterate over the entries using a for...of loop, accessing each key and value directly from the iterable.
We print each key and value to the console using the console.log function to verify that we are iterating over all entries.

JavaScript Program

const myMap = new Map([
    ['one', 1],
    ['two', 2],
    ['three', 3]
]);

// Iterate over entries using for...of loop
for (const [key, value] of myMap.entries()) {
    console.log(`Key: ${key}, Value: ${value}`);
}

Output

Key: one, Value: 1
Key: two, Value: 2
Key: three, Value: 3

2 Iterating Over Entries Using forEach Method

We can iterate over entries in a map in JavaScript using the forEach method, which provides a flexible way to access each key-value pair in the map.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We use the forEach method to iterate over the key-value pairs in the map.
In the callback function passed to forEach, we access each key and value.
We print each key and value to the console using the console.log function to verify that we are iterating over all entries.

JavaScript Program

const myMap = new Map([
    ['one', 1],
    ['two', 2],
    ['three', 3]
]);

// Iterate over entries using forEach method
myMap.forEach((value, key) => {
    console.log(`Key: ${key}, Value: ${value}`);
});

Output

Key: one, Value: 1
Key: two, Value: 2
Key: three, Value: 3

3 Storing and Iterating Over Entries Separately

We can store entries in a separate array and then iterate over the array in JavaScript, which provides a way to work with key-value pairs independently of the map.

For example,

We start by declaring and initializing a map named myMap with some key-value pairs. In this example, the map has string keys and integer values.
We declare an array named entries to store the key-value pairs from the map.
We use the entries method to get an iterable of the key-value pairs in the map and spread it into the entries array using the spread operator.
We use a for loop to iterate over the entries array and print each key and value to the console using the console.log function to verify that we have stored all entries separately.

JavaScript Program

const myMap = new Map([
    ['one', 1],
    ['two', 2],
    ['three', 3]
]);

// Store entries in a separate array
const entries = [...myMap.entries()];

// Iterate over the entries array
for (const [key, value] of entries) {
    console.log(`Key: ${key}, Value: ${value}`);
}

Output

Key: one, Value: 1
Key: two, Value: 2
Key: three, Value: 3

Summary

In this tutorial, we learned How to Iterate Over Entries (Key-Value Pairs) in a Map in JavaScript language with well detailed examples.

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