Working with Arrays, Loops, and Conditional Statements - HTML, CSS, and Dynamic HTML - page 843

Putting all of these expressions together, you get the following for loop:

for (var i = 0; i < 4; i++) {
commands
}
The collection of commands that is run each time through a loop is collectively known
as a command block , a feature you've already worked with in functions. A command
block is indicated by its opening and closing curly braces { }. The following is an
example of a for loop that writes the value of the counter variable to a table cell on
the Web page:

for (var i = 0; i < 4; i++) {
document.write(“<td>” + i + “</td>”);
}
As shown in Figure 12-12, each time through the loop, the value displayed in the table
cell is changed by 1.

Figure 12-12 viewing a for loop

continue
if true

starting value
of the counter
variable

update after
each loop

Counter Values Code Written

to the Page

0 <td> 0 </td>

<td> 1 </td>
<td> 2 </td>
<td> 3 </td>

1
2
3

One for loop can be nested within another. Figure 12-13 shows the code used to
create a table with three rows and two columns. This example uses two counter variables
named rowNum and colNum . The rowNum variable loops through the values 1, 2, and
3; and for each of those values, the colNum variable loops through the values 1 and 2.
Each time the value of the colNum variable changes, a new cell is added to the table.
Each time the value of the rowNum variable changes, a new row is added to the table.