One of the most common uses of a for loop is to carry out a task once for each item in a collection. We have learned about two types of collections, strings and arrays. When using a loop with a collection in this way, we say that the loop iterates over the collection.
The following example prints each of the characters of the string "LaunchCode" on a separate line.
Example
1let name = "LaunchCode";
2
3for (let i = 0; i < name.length; i++) {
4 console.log(name[i]);
5}
Console Output
L
a
u
n
c
h
C
o
d
e
Since name.length is 10, the loop executes once each for the values of i from 0 to 9. The loop body, console.log(name[i]);, will print name[i] each time. In each case, name[i] is one of the characters of name.
Try It!
Write a program that prints each character of your name on a different line.
1// create a string variable containing your name
2
3// write a for loop that prints each character in your name on a different line
The following example prints each of the programming languages in the array languages on a separate line.
Example
1let languages = ["JS", "Java", "C#", "Python"];
2
3for (let i = 0; i < languages.length; i++) {
4 console.log(languages[i]);
5}
Console Output
JS
Java
C#
Python
Similar to the string example, this loop executes 4 times because
languages.length is 4. For each iteration, languages[i] is one of the
items in the array and the given language is printed.
Try It!
Write a program that prints the name of each member of your family on a different line.
1// create an array variable containing the names
2
3// write a for loop that prints each name on a different line