Extract all map keys with a specific value in JavaScript

This post will discuss how to extract all keys with a specific value from a Map in JavaScript.

To extract all keys with a specific value from a Map in JavaScript, we need to iterate through the map entries and compare the values with the given value using strict equality operator (===). We can use different functions to do this, such as:

1. Using `Map.forEach()` function

The Map.forEach() function executes a callback function for each entry in the map. The callback function can access the key and the value of the current pair and check if the value matches the given value. If it does, it can add the key to an array of keys. For example, we can use the following code snippet to retrieve all keys having the value 4 in a map:

// Create a map

let map = new Map ([['a', 1], ['b', 2], ['c', 4], ['d', 4], ['e', 3]]);

// the value to search for

let value = 4;

// retrieve all keys having the given value

let keys = [];

map.forEach ((v, k) => {

if (v === value) {

keys.push(k);

}

});

// Log the keys

console.log(keys); // ['c', 'd']

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Alternatively, we can use for…of loop to iterates over the maps. We can use this loop to access the key and value of each entry in the map and compare the value with the given value. If they match, we can add the key to an array. The following code illustrates this:

// Create a map

let map = new Map ([['a', 1], ['b', 2], ['c', 4], ['d', 4], ['e', 3]]);

// the value to search for

let value = 4;

// retrieve all keys having the given value

let keys = [];

for (let [k, v] of map) {

if (v === value) {

keys.push(k);

}

// Log the keys

console.log(keys); // ['c', 'd']

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2. Using `Array.filter()` function

The idea is to convert the map into an array of key-value pairs using the Array.from() function or the spread operator (…). Then we can use Array.filter() function to filter out the key-value pairs that have the given value in the map. The filter function creates a new array with all elements that pass a test implemented by a callback function. Finally, we can use the Array.map() function to extract only the keys from the filtered array. Here’s an example:

// Create a map

let map = new Map ([['a', 1], ['b', 2], ['c', 4], ['d', 4], ['e', 3]]);

// the value to search for

let value = 4;

// Convert the map into an array of entries

const entries = Array.from(map);

// Filter the entries by value and map them to keys

const keys = entries.filter(([k, v]) => v === value)

.map(([k]) => k);

// Log the keys

console.log(keys); // ['c', 'd']

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3. Using a custom function

Finally, we can use a custom function that takes a map and a value as parameters and returns an array of keys. This is a more reusable and modular way, but it requires us to write and maintain our own function. This works well if we need more control over how the values are compared or if we want to reuse the function for different maps and values. However, it does not work if we want to use a more concise or functional style of coding. Here’s an example of how we can achieve this:

// Create a custom function

function getKeysByValue(map, value)

{

// Initialize an empty array

const keys = [];

// Loop through the map entries

for (let [k, v] of map)

{

// Check if the value matches the given value

if (v === value) {

// Push the key into the array

keys.push(k);

}

// Return the array

return keys;

}

// Create a map

let map = new Map ([['a', 1], ['b', 2], ['c', 4], ['d', 4], ['e', 3]]);

// the value to search for

let value = 4;

// Call the function with the map and the value

const keys = getKeysByValue(map, value);

// Log the keys

console.log(keys); // ['c', 'd']

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That’s all about extracting all keys with a specific value from a Map in JavaScript. All above functions works well for maps that contain primitive values, such as numbers, strings, booleans, etc.

Extract all map keys with a specific value in JavaScript

1. Using Map.forEach() function

2. Using Array.filter() function

3. Using a custom function

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1. Using `Map.forEach()` function

2. Using `Array.filter()` function