How to Set a Default Value for a Key in a Map in JavaScript - Step by Step Examples

How to Set a Default Value for a Key in a Map in JavaScript ?

Answer

To set a default value for a key in a map in JavaScript, you can use the set method combined with the has method. This approach involves checking if the key exists in the map using the has method. If the key does not exist, you can then use the set method to insert the key with the specified default value. This ensures that the key is only added to the map if it is not already present, preventing overwriting any existing values associated with the key. This technique is useful for initializing map entries with default values in scenarios where the map might not have pre-existing entries for certain keys.

✐ Examples

1 Setting a Default Value Using has and set Methods

We can set a default value for a key in a map in JavaScript by checking if the key exists using the has method and then using the set method to insert the key-value pair if the key does not exist.

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 has method to check if the key exists in the map. If the key does not exist, we use the set method to insert the key with the default value.
We print the updated map to the console using the forEach method and console.log.

JavaScript Program

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

// Set a default value using has and set methods
if (!myMap.has('four')) {
    myMap.set('four', 4);
}

// Print the updated map
myMap.forEach((value, key) => {
    console.log(`${key}: ${value}`);
});

Output

one: 1
two: 2
three: 3
four: 4

2 Setting a Default Value Conditionally Using has and set Methods

We can set a default value for a key in a map in JavaScript by using the has method to check if the key exists and then using the set method to insert the key-value pair if the key does not exist, based on a condition.

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 has method to check if the key exists in the map. If the key does not exist, we use the set method to insert the key with the default value based on a condition.
We print the updated map to the console using the forEach method and console.log.

JavaScript Program

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

// Set a default value conditionally using has and set methods
if (!myMap.has('four')) {
    myMap.set('four', myMap.get('four') || 4);
}

// Print the updated map
myMap.forEach((value, key) => {
    console.log(`${key}: ${value}`);
});

Output

one: 1
two: 2
three: 3
four: 4

3 Setting Multiple Default Values Using has and set Methods

We can set multiple default values for keys in a map in JavaScript by using the has method to check if the keys exist and then using the set method to insert the key-value pairs if the keys do not exist.

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 has method to check if the keys exist in the map. If the keys do not exist, we use the set method to insert the keys with the default values.
We print the updated map to the console using the forEach method and console.log.

JavaScript Program

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

// Set multiple default values using has and set methods
if (!myMap.has('four')) {
    myMap.set('four', 4);
}
if (!myMap.has('five')) {
    myMap.set('five', 5);
}

// Print the updated map
myMap.forEach((value, key) => {
    console.log(`${key}: ${value}`);
});

Output

one: 1
two: 2
three: 3
four: 4
five: 5

Summary

In this tutorial, we learned How to Set a Default Value for a Key in a Map in JavaScript language with well detailed examples.

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How to Set a Default Value for a Key in a Map in JavaScript - Step by Step Examples