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The returning value The first difference between map() and forEach() is the returning value. The forEach() method returns undefined and map() returns a new array with the transformed elements. Even if they do the same job, the returning value remains different.
The main difference between forEach and filter is that forEach just loop over the array and executes the callback but filter executes the callback and check its return value.
The map() method, similar to the forEach() method, executes the provided function once for each element in an array. But unlike the forEach() method, it creates a new array with the results of calling a function for every array element. Hence map() method relies on immutability.
Final Thoughts. You can use both map() and forEach() interchangeably. The biggest difference is that forEach() allows the mutation of the original array, while map() returns a new array of the same size. map() is also faster.
The difference is in the return values.
.map() returns a new Array of objects created by taking some action on the original item.
.every() returns a boolean - true if every element in this array satisfies the provided testing function. An important difference with .every() is that the test function may not always be called for every element in the array. Once the testing function returns false for any element, no more array elements are iterated. Therefore, the testing function should usually have no side effects.
.forEach() returns nothing - It iterates the Array performing a given action for each item in the Array.
Read about these and the many other Array iteration methods at MDN.
gilly3's answer is great. I just wanted to add a bit of information about other types of "loop through elements" functions.
.every() (stops looping the first time the iterator returns false or
something falsey).some() (stops looping the first time the iterator
returns true or something truthy).filter() (creates a new array
including elements where the filter function returns true and
omitting the ones where it returns false).map() (creates a new array from the values returned by the iterator
function).reduce() (builds up a value by repeated calling the iterator,
passing in previous values; see the spec for the details; useful
for summing the contents of an array and many other things).reduceRight() (like reduce, but works in descending rather than
ascending order)credit to: T.J.Crowder For-each over an array in JavaScript?
Another consideration to the above great answers is chaining. With forEach() you can't chain, but with map(), you can.
For example:
var arrayNumbers = [3,1,2,4,5];
arrayNumbers.map(function(i) {
return i * 2
}).sort();
with .forEach(), you can't do the .sort(), you'll get an error.
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