What is the Difference Between Map and Object in JavaScript, and Why Do We Need Map?

February 13, 2023

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ES6 introduced the Map object, which allows developers to work with key-value pairs. However, plain JavaScript objects can also be used for this purpose. So, why do we need the Map object, and what problems does it solve?

Objects Can Only Use Strings as Keys, While Maps Can Use Anything

When working with key-value pairs, developers often use various types of keys. However, in JavaScript, if you use a plain object, any key you use will be converted into a string. This can often cause errors, such as when two different keys are converted into the same string, causing a collision. The Map object, on the other hand, allows developers to use any type of key.

Objects Do Not Support Iteration, While Maps Do

In the past, we couldn't directly iterate over a plain JavaScript object using for...of or forEach. We needed to use additional methods like Object.entries and Object.keys to assist us. However, the Map object is iterable, so we can directly use for...of or forEach with it.

Objects Have No Order, While Maps Maintain Order

As mentioned earlier, the Map object is iterable, and it has the advantage of maintaining order while iterating. In the past, iterating through a plain object using object methods like Object.entries and Object.keys did not necessarily return the key-value pairs in the same order in which they were entered. In some cases, such as when writing algorithms, maintaining order is essential, making the Map object much more useful.

Map Provides Many Common Key-Value Pair Methods That Objects Do Not

For example, if we want to know the size of a key-value pair, Map has a size method that is simple and easy to use. In contrast, if we use a plain object, we may need to use Object.keys and then use .length to find out how many keys are in the object. This can be much more cumbersome. Additionally, Map provides a clear method that allows us to delete all key-value pairs at once, whereas we would need to delete each pair individually in a plain object.

In addition to the points mentioned above, there are other subtle differences between Map and plain objects, and their performance varies in different contexts. Interested readers are encouraged to read the following articles:

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