Filter a Map in JavaScript

This post will discuss how to filter a map in JavaScript.

Filtering a map means creating a new map or updating the existing map to contains only the key-value pairs that satisfy a certain condition. Here are some of the methods we can use to filter a map in JavaScript:

1. Using `Array.filter()` function

The Array.filter() function creates a new array with only the elements that pass a test function. The spread operator (…) or Array.from() function converts a map into an array of [key, value] pairs. We can use these functions together to create a new array of [key, value] pairs that meet the condition, and then convert it back to a map using the Map() constructor. The following code illustrates this:

// Create a map of names and ages

const map = new Map([["Thomas", 25], ["Samuel", 30], ["Christopher", 15]]);

// Define a condition function

function isAdult([key, value]) {

return value >= 18;

}

// Convert the map to an array and filter it by the condition

const filteredArray = [...map].filter(isAdult);

// Convert the filtered array back to a map

const filteredMap = new Map(filteredArray);

// The filtered map contains only the pairs that meet the condition

console.log(filteredMap); // Map(2) { 'Thomas' => 25, 'Samuel' => 30 }

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2. Using `Map.forEach()` and `Map.delete()` function

The Map.forEach() function iterates over the key-value pairs in the map and executes a callback function for each pair. The Map.delete() function removes a key-value pair from the map by its key. We can use these functions together to delete the key-value pairs that do not meet the condition from the original map. The following code illustrates this:

// Create a map of names and ages

const map = new Map([["Thomas", 25], ["Samuel", 30], ["Christopher", 15]]);

// Define a condition function

function isAdult(value, key, map) {

return value >= 18;

}

// Iterate over the map and delete the pairs that do not meet the condition

map.forEach((value, key, map) => {

if (!isAdult(value, key, map)) {

map.delete(key);

}

});

// The map now contains only the pairs that meet the condition

console.log(map); // Map(2) { 'Thomas' => 25, 'Samuel' => 30 }

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That’s all about filtering a map in JavaScript.

Filter a Map in JavaScript

1. Using Array.filter() function

2. Using Map.forEach() and Map.delete() function

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1. Using `Array.filter()` function

2. Using `Map.forEach()` and `Map.delete()` function