/*
 * title "Array.prototype.arrayLength"
 * author "Dylan Lom"
 * date "2022-08-05"
 * link stylesheet "/main.css"
 */

# $(echo $title)

An exercise in stupidity

> How do you get the length of an array in JavaScript?

<pre><code>
Array.prototype.arrayLength = function () { return this.length }
</code></pre>

> I don't trust <insert-js-impl-here>

<pre><code>
Array.prototype.arrayLength = function() {
    let len = 0
    for (let x in this) {
        if (len === 0) len++
        len++
    }
    return len
}
</code></pre>

*Aside: I think I'd had too much to drink by this point -- the above implementation*
*is just wrong. Also amusingly iterating `this` actually includes `arrayLength`, which*
*I can't quite explain currently (I guess I'm using prototype wrong?)*

> Ok, but that could you make it look like "modern" js at least?

<pre><code>
Array.prototype.arrayLength = function() {
    let len = 0
    this.forEach((x, i) => len = i + 1)
    return len
}
</code></pre>

> Surely you don't need three lines?

<pre><code>
Array.prototype.arrayLength = function() {
    return this.reduce(acc => acc+1, 0)
}
</code></pre>

> Sorry but that implementation does not account for setting 
> arbitrary indecies:
>
> <pre><code>
> const xs = [1,2,3]
> xs[99] = 100
> xs.length == 100
> xs.arrayLength() == 4
</pre></code></pre>
>

**N.B.**: The `for (const x in this)` solution fails at this as well

<pre><code>
Array.prototype.arrayLength = function() {
    return Math.max(...Object.keys(this).map(x => Number.parseInt(x)).filter(k => !Number.isNaN(k))) + 1
}
</code></pre>

> *Clears throught* `[].arrayLength() === -Infinity`

<pre><code>
Array.prototype.arrayLength = function() {
    return (Object.keys(this).map(x => Number.parseInt(x)).filter(k => !Number.isNaN(k)).sort((a, b) => b - a)[0]) + 1 || 0
}
</code></pre>

> I hate you

<pre><code>
Array.prototype.arrayLength = function() {
    return this.findLastIndex(this.at(-1))
}
</code></pre>

> *Cries in non-bleeding-edge-impl*

**N.B.**: I haven't even tested this implementation, since I don't have
any javascripts that support findLastIndex currently.

## Footnote

I actually learnt something about how `.forEach` was implemented by thinking up
and testing these dumb implementations, how novel!

<pre><code>
Array.prototype.myForEach = function(f) {
    const kvs = Object.entries(this).filter(([k]) => !Number.isNaN(Number.parseInt(k)))
    for (let i = 0; i < kvs.length; i++) {
        f(kvs[i][1], Number.parseInt(kvs[i][0]))
    }
}
</code></pre>

It's quite interesting how far we go in pretending that the numeric indecies we
pass in square-braces are actually numbers -- ie. we pass back the numeric
index in the forEach. Or maybe I just don't quite understand it

<pre><code>
const xs = [1,2,3]
xs[1] === xs['1']
</code></pre>