Limited Lives - Building JavaScript Games for Phones, Tablets, and Desktop - page 132

This is a very compact instruction that increments the counter and draws the sprite at different
positions. This instruction is equivalent to the following while instruction:

var i = 0;
while (i < this.lives) {
Canvas2D.drawImage(sprites.lives,
new Vector2(i * sprites.lives.width + 15, 60));
i = i + 1;
}

And here's another example:

for (var i = this.lives - 1; i >=0; i--)
Canvas2D.drawImage(sprites.lives,
new Vector2(i * sprites.lives.width + 15, 60));

To which while instruction is this for instruction equivalent? Does it make a difference in practice
whether you increase or decrease the counter in this case? Figure 10-3 contains the syntax diagram
of the for instruction.

for instruction

for ( expression ;

,

declaration

expression ; expression ) instruction

,

Figure 10-3. Syntax diagram of the for instruction

A Few Special Cases
There are a few special cases that you need to know about when dealing with while and for loops.
The following subsections discuss these cases.

No Repeat at All
Sometimes the condition in the header of a while instruction is already false at the beginning.
Look at the following code fragment:

var x = 1;
var y = 0;
while (x < y)
x++;