tedx presentation: diamond shape problem

diamond.js

// usage:
// node diamond.js 8
//
const length = parseInt(process.argv.slice(2)[0]);
const char = '*';
const space = ' ';
const newLine = '\n';
const TWO = 2;

var charCount = 1;
var spaceCount = length - 1;
var adding = true;

process.stdout.write(newLine);

for (var i = 0; i < length; i++) {
    drawLine(spaceCount, charCount);
    charCount = charCount + TWO;
    spaceCount--;
}

charCount = charCount - TWO;
spaceCount++;

for (var i = 0; i < length - 1; i++) {
    charCount = charCount - TWO;
    spaceCount++;
    drawLine(spaceCount, charCount);
}

process.stdout.write(newLine);

function drawLine(spaceCount, charCount) {
    for (var i = 0; i < spaceCount; i++) {
        process.stdout.write(space);
    }
    for (var i = 0; i < charCount; i++) {
        process.stdout.write(char);
    }
    process.stdout.write(newLine);
}

As featured in my TEDx talk:
https://www.youtube.com/watch?v=x77-gT8bWLo