forEach
- Dart course
- Intermediate
- Lesson 50/116
- 5 min
Learn side-effect loops with forEach.
The forEach method
The forEach method performs an action for each element but returns nothing. It is used for side effects; for example printing each element.
Example: ['Apple', 'Banana', 'Cherry'].forEach((f) => print(f));. This prints each fruit on a separate line. Unlike map, forEach produces no result.
forEach replaces a loop. The code becomes shorter and more readable. But because it has no return value it cannot be chained.
forEach vs map
forEach and map look similar but serve different purposes. map returns a transformed collection; forEach returns nothing.
For side effects like printing use forEach. When you need transformed data use map. The wrong choice does not break the code but hurts readability.
Example: fruits.forEach((f) => print(f)); prints each fruit. fruits.map((f) => f.length) returns a list of lengths.
Practice Print the fruits
Call forEach on the list ['Apple', 'Banana', 'Cherry']. Print each fruit with a 'Fruit: ' prefix; for example Fruit: Apple.
Starter code
void main() {
var fruits = ['Apple', 'Banana', 'Cherry'];
// use .forEach to print each fruit with a 'Fruit: ' prefix
}Sample solution
void main() {
var fruits = ['Apple', 'Banana', 'Cherry'];
fruits.forEach((f) => print('Fruit: $f'));
}Expected output
Fruit: Apple Fruit: Banana Fruit: Cherry
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does forEach return?
var a = [1, 2, 3].forEach((n) => print(n));- A new list
- void (returns nothing) Correct answer
- An Iterable
- A number
Explanation: forEach returns nothing, it is void.
2 Match the forEach parts
| Term | Meaning |
|---|---|
(m) => print(m) |
Side effect function |
.forEach(...) |
Call |
void |
Return type |
print(m) |
Print action |
3 The forEach call
var fruits = ['Apple', 'Banana', 'Cherry'];
fruits.____((f) => print('Fruit: $f'));var fruits = ['Apple', 'Banana', 'Cherry'];
fruits.forEach((f) => print('Fruit: $f'));Explanation: forEach performs an action per element.