read PNG magic.

pngreader.ts

/**
 * read PNG file.
 */
import * as fs from 'fs';

function putUsage(): void
{
	const usage = "Usage: node pngreader.ts source.png";
	console.log(usage);
}

if (process.argv.length < 3) {
	putUsage();
	process.exit(0);
}

const sourcePath = process.argv[2];

fs.open(sourcePath, 'r', function (err, fd) {
	let buffer = new Buffer(4);

	fs.read(fd, buffer, 0, 4, null, function (err, bytesRead, buffer) {
		console.log(buffer);
		let png_p: boolean = (
			buffer[0] == 0x89 &&
			buffer[1] == 0x50 && // P
			buffer[2] == 0x4e && // N
			buffer[3] == 0x47 ); // G
		console.log('This is ' + (png_p ? '' : 'not ') + 'PNG file!');
	});
});