Implement program flow - Programming in HTML5 with JavaScript and CSS3 - page 129

This code processes the code block, and then while an expression is true, continues to
process this code block. The following code segment demonstrates this:
var canvas = document.getElementById("canvas1");
do {
//stop traffic
}while(canvas.styles.backgroundColor == 'red')
In this code segment, the logic to stop traffic runs one time. Then, it evaluates the
expression that checks whether the background of the canvas is red. The loop continues to
run as long as this expression evaluates to true .
Short-circuiting the loops
Two mechanisms enable you to short-circuit a loop. The break keyword exits the current loop
completely, whereas the continue keyword breaks out of the code block and continues to the
next iteration of the loop.
EXAM TIP
The break keyword breaks out of only the currently running loop. If the loop containing
the break is nested inside another loop, the outer loop continues to iterate as controlled by
its own expression.
Thought experiment
Identifying subtleties in syntax
In this thought experiment, apply what you've learned about this objective. You can
find answers to these questions in the “Answers” section at the end of this chapter.
Various constructs perform the same function but with a different syntax. For
example, the real difference between a switch statement and nested if…else state-
ments is minimal. Also, the while and for loops both evaluate a condition to know
whether the loop should proceed.
1. When is a for loop better than a while loop?
2. How is the readability of the code affected?
Objective summary
■ The for and for…in iterate for a known length of values.
■ The while and do…while loops run until a Boolean condition is set to false .
■ Arrays provide a mechanism in which to create lists of things.