javascript

CHAPTER 4 ■ CONTROLLING FLOW
122
Writing a do while loop
while loops provide a way to conditionally run a path zero or more times. That is, if the loop expression
equates to false when it is first evaluated, then the path will not run at all. Now what if you want to make
sure the path runs at least one time? For this circumstance, you would write a do while loop. The syntax
for do while is as follows:
do path while (expression);
As you might guess by now, path can be either a single child statement or a block, and the value of
expression is converted to a boolean if necessary by passing it to Boolean(). Though it is easy to
overlook, the semicolon following the expression in parentheses is required. With those things in mind,
click Clear in both Firebug panels, and let’s try a do while loop.
More often than not, when it comes time to follow a recipe, there is a spice that if unavailable would
put the kaibosh on my plans. Say I want to make lemon scones; the limiting ingredient would be, oddly
enough, lemon peel. Being a foodie, it is safe to assume I have at least one spice. Therefore, it makes
sense to rummage through the spice shelf with a do while loop like so, because we want to check at least
one spice:
var spices = [
"cinnamon",
"ginger",
"nutmeg",
"cloves",
"sesame seed",
"pepper",
"rosemary",
"tarragon",
"basil",
"mace",
"poppy seed",
"lemon peel",
"vanilla",
"oregano",
"allspice",
"thyme"
];
var putTheKaiboshOn = true;
var i = 0;
do {
if (spices[i] === "lemon peel") {
putTheKaiboshOn = false;
break;
}
i ++;
} while (i < spices.length);
(putTheKaiboshOn) ? "No can do!" : "Go right ahead!";
// "Go right ahead!"
Verify your work with Figure 4–11.