Differences between .forEach() and .map()

When a programmer is working with arrays in JavaScript there are two commonly used array methods, ".forEach()" and ".map()". At first glance they may seem pretty similar but there are a few key differences between them. These differences can greatly impact how one would transform and manipulate arrays. This post will be going over the differences between the two and understanding when you would use each method.

The purpose and functionality are the main differences. ".forEach()" is an array method that will iterate over each element in an array and then will perform a specified action on each element in the array. ".forEach()" will not return a new array and it is primarily used for executing side effects/operations that don't require a transformed array. ".map()" also iterates over each element in an array. The reason it differs from ".forEach()" is because it returns a new array with the exact length as the original array. ".map()" is most commonly used for transforming or mapping elements from one array to another array.

The return values also differentiate ".map()" and ".forEach()". With return values ".forEach()" does not return anything, all it does is simply execute the provided callback function for each element in the array. ".map()" actually will return a new array. It will allow one to create a new array based on the transformation logic defined in within the callback function.

Another difference is how each method will handle side effects and the purpose they serve. ".forEach()" is good to use when one wants to perform an action on each element of an array without creating a whole new array. One example would be using ".forEach()" to log each element to the console. ".map()" is useful when one would want to create a new array with modified changes. This allows you to perform transformations on each element and then collect the results in a new array.

The mutability of the original array is also another difference. ".forEach()" does not modify the original array. It only operates on the elements in the array and it does not change their order or values. ".map()" will return a new array but leave the original array unchanged. This ensures that the original array remains the same while the new array will be transformed.

In conclusion the main differences between ".forEach()" and ".map()" are their pruposes, return values, how they handle side effects, and the impact on the original array. ".forEach()" is mainly used for executing operations on elements in an array without returning a new array. ".map()" is mainly used when transforming or mapping elements from one array to another by creating a whole new array. Understanding the differences will help one make informed decisions when working with arrays. Remember to use ".forEach()" for operations and side effects without returning a new array. Make sure to use ".map()" to create a whole new array which has transformed values from the original array.