The Book of JavaScript, 2nd Edition

Loops Can Nest

Just as you can nest if-then statements inside other if-then statements, you can also put loops inside other loops. For example, Figure 8-15 shows you a script that writes a solid rectangle of Xs to a web page, five Xs high and ten Xs wide (see the result in Figure 8-16). Although this script doesn't do anything useful, it offers an idea of how nesting loops work.

Figure 8-15. A simple example of nesting loops

Line ❶ in Figure 8-15 sets up a loop that will be executed five times. Each time through that loop, the second, or inner, loop (❷ and ❸) runs. That loop writes the letter X to the web page ten times. After the inner loop has run, ...