text: 
  const cp = require('child_process');
  const nlane = require('../');
  
  
  async function test1()
  {
  	// define `polaroid' function.
  	function polaroid(src, dst)
  	{
  		return new Promise( (resolve,reject) => {
  			cp.execFile(
  				'convert', [src, '-background', '#cc0000', '-polaroid', '5', dst],
  				(err, stdout, stderr) => {
  					if (err) reject(err);
  					else resolve();
  			});
  		});
  	}
  
  	// make narrow-laned function `nlpolaroid` from the `polaroid'.
  	var lane = new nlane.lane(3);
  	var nlpolaroid = lane.narrowifyPromised(polaroid);
  
  	// call `nlpolaroid' fifteen times consecutively.
  	var p = [];
  	for ( i=0; i<15; i++ )
  	{
  		p.push( nlpolaroid("canvas.jpg", `polaroid${i}.jpg`) );
  	}
  
  	// wait all asynchronous process.
  	try {
  		await Promise.all(p);
  		console.log(`finished. `);
  	} catch (e) {
  		console.log(`error. ${e}`);
  	}
  };
  
  cp.execFile('convert',
  	['-size', '1920x1080', 'xc:white', 'canvas.jpg'],
  	(err,stdout,stderr) => {
  		if(err) console.log('error: You have to install imagemagick for this example.');
  		else test1();
  	});
  
  