Apollolux: created

2013-06-15T00:44:40Z

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Here's a bunch of enemies we're fighting against:
<syntaxhighlight>
var enemies = [
{name: "Duck", hp: 10},
{name: "Duck", hp: 10},
{name: "Goose", hp: 15}
];
</syntaxhighlight>

Let's kill them off:
<syntaxhighlight>
forEach(enemies, function (enemy) {
enemy.hp = 0;
});
</syntaxhighlight>

Now they're all dead.

Our problem is to find out when every enemy's HP has dropped to zero.
===The chump's way===
<syntaxhighlight>
var allDead = true;
for (var i = 0; i < enemies.length; ++i) {
if (enemies[i].hp > 0)
allDead = false;
}
</syntaxhighlight>

This presents another problem which isn't in the previous example: what if the variable <var>i</var> is being used for something? Battle systems tend to occur in loops, and for all we know, that loop could be using <var>i</var>. We could shift onto variable <var>j</var>, and then future code changes would move into variable <var>k</var>... and it goes on. What a mess.

Another problem was developing the algorithm itself: I had to stop and think, how should I do this?

# Should <var>allDead</var> start false and turn into true when going through the loop and discovering all enemies are dead?
# Should <var>allDead</var> start true and turn into false when discovering a single living enemy?

I got side-tracked by the "how", and lost sight of the "what".

===A smarter way===
We could take advantage of our higher-order functions to express our intent more clearly:
<syntaxhighlight>
var allDead = filter(function (enemy) {
return enemy.hp > 0;
}, enemies).length === 0;
</syntaxhighlight>

This is easy to read: we filter through all enemies to get all the living ones in an array. If the length of that array is 0, they're all dead. Again, shorter and a lot easier to read.

Note also that it expresses what I was after: all enemies are dead if the length of living enemies found is zero.

JavaScript/Higher-order programming/Example 3 - Revision history

Apollolux: created