Remove entries with null values from a Map in JavaScript

This post will discuss how to remove entries with null values from a Map in JavaScript.

To remove entries with null values from a map in JavaScript, we need to iterate through the map entries and delete the entries that have a null value. 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. We can use this function to check the value of each entry and delete it if it is null. For example, we can use the following code snippet to remove entries with null values from a map:

// Create a map

let map = new Map ([['a', 1], ['b', null], ['c', 5], ['d', null], ['e', 3]]);

// Loop through the map entries

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

// Check if the value is null

if (value === null) {

// Delete the entry from the map

map.delete(key);

}

});

// Map(3) { 'a' => 1, 'c' => 5, 'e' => 3 }

console.log(map);

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Alternatively, we can use the for…of loop to access the key and value of each entry in the map and delete it if the value is null. For example, we can use the following code snippet to remove entries with null values from a map:

// Create a map

let map = new Map ([['a', 1], ['b', null], ['c', 5], ['d', null], ['e', 3]]);

// Loop through the map entries

for (let [key, value] of map) {

// Check if the value is null

if (value === null) {

// Delete the entry from the map

map.delete(key);

}

// Map(3) { 'a' => 1, 'c' => 5, 'e' => 3 }

console.log(map);

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This is the simplest and most straightforward way, but it requires us to mutate the original map and use the delete operator. However, it does not work to create a new map without null values.

2. Using `Array.filter()` function

We can use the Array.from() function to convert the map into an array of entries and use the Array.filter() function to remove the ones with null values. Then use the new Map() constructor to create a new map from the filtered array. This is a more functional and concise way, but it requires us to create two intermediate arrays and use arrow functions. This approach is preferred to create a new map without null values, and prefer a more declarative and expressive style of coding. For instance:

// Create a map

let map = new Map ([['a', 1], ['b', null], ['c', 5], ['d', null], ['e', 3]]);

// Convert the map into an array of entries

const entries = Array.from(map);

// Filter the entries by value

const filtered = entries.filter(([key, value]) => value !== null);

// Create a new map from the filtered array

const newMap = new Map(filtered);

// Map(3) { 'a' => 1, 'c' => 5, 'e' => 3 }

console.log(newMap);

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3. Using a custom function

Use a custom function that takes a map as a parameter and returns a new map without null values. This is a more reusable and modular way, but it requires us to write and maintain our own function. For instance:

// Create a custom function

function removeNullValues(map) {

// Initialize an empty array

const filtered = [];

// Loop through the map entries

for (let [key, value] of map) {

// Check if the value is not null

if (value !== null) {

// Push the entry into the array

filtered.push([key, value]);

}

// Create a new map from the filtered array and return it

return new Map(filtered);

}

// Create a map

let map = new Map ([['a', 1], ['b', null], ['c', 5], ['d', null], ['e', 3]]);

// Call the function with the map

const newMap = removeNullValues(map);

// Map(3) { 'a' => 1, 'c' => 5, 'e' => 3 }

console.log(newMap);

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This method works well if we need more control over how the values are compared or to reuse the function for different maps. However, it does not work to modify the original map or to use a more concise or functional style of coding.

That’s all about removing entries with null values from a Map in JavaScript.

Remove entries with null values from a Map 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