Storing and Recalling Game Data - Building JavaScript Games for Phones, Tablets, and Desktop - page 275

The switch instruction has a few handy properties that make it very useful for handling different
alternatives. Have a look at the following code example:
if (x === 1)
one();
else if (x === 2) {
two();
alsoTwo();
} else if (x === 3 || x === 4)
threeOrFour();
else
more();
You can rewrite this with a switch instruction as follows:
switch(x) {
case 1: one();
break;
case 2: two();
alsoTwo();
break;
case 3:
case 4: threeOrFour();
break;
default: more();
break;
}
When a switch instruction is executed, the expression between the parentheses is calculated.
Then the instructions after the word case and the particular value are executed. If there is no case
that corresponds to the value, the instructions after the default keyword are executed. The values
behind the different cases need to be constant values (numbers, characters, strings between double
quotes, or variables declared as constant).
The break Instruction
If you aren't careful, the switch instruction will execute not only the instruction behind the relevant
case but also the instructions behind the other cases. You can prevent this by placing the special
break instruction after each case. The break instruction basically means, “Stop executing the
switch , while , or for instruction you're currently in.” If there was no break instruction in the previous
example, then in the case x === 2 , the methods two and alsoTwo would be called, and also the
methods threeOrFour and more .
In some cases this behavior is useful, so that, in a sense, the different cases flow through each
other. You have to watch out when doing this, though, because it can lead to errors—for instance,
if a programmer forgot to place a break instruction somewhere, this would lead to very strange
behavior. When you use the switch instruction, do it in such a way that cases are always separated
by break instructions. The only exception is when you write multiple case labels in front of a group