Strange behaviour of node-canvas that I can't understand. I expect this code to write 10 .png files each of which contains a "Page [n]" text. Instead, I get one .png only called page11.png (??? the last should be 10) with "Page 8" in it! There must be something about timing that I am missing.

package.json

{
  "name": "test",
  "version": "0.0.1",
  "author": "Gianfranco Cecconi <gianfranco.cecconi@digitalcontraptionsimaginarium.co.uk>",
  "description": "Does what it says on the tin",
  "contributors": [ 
    {
      "name": "Gianfranco Cecconi",
      "email": "gianfranco.cecconi@digitalcontraptionsimaginarium.co.uk"
    } 
  ],
  "keywords": [
    "test"
  ],
  "dependencies" : {
    "canvas": ">=1.1.1",
    "optimist": ">=0.6.0"
  },
  "license": "MIT",
  "engines": {
    "node": ">=0.10.18"
  }
}

test.js

var fs = require('fs'),
	Canvas = require('canvas'),
	argv = require('optimist') 
		.usage('Usage: $0 --out [output folder]')
		.demand([ 'out' ])
		.alias('out', 'o')
		.argv;

for(var page = 1; page <= 10; page++) {
	var canvas = new Canvas(200, 200),
	  	ctx = canvas.getContext('2d');
	ctx.font = '30px Impact';
	ctx.fillText("Page " + page, 50, 100); 
	canvas.toBuffer(function (err, buf) {
		if (err) throw err;
		fs.writeFile(argv.out + '/page' + page + '.png', buf);
	});
}