Design Pattern: Decorator Pattern - Javascript Solution

decorator_pattern.js

let fs = require('fs');

// ConcreteComponent
class SimpleWriter {
	constructor(path) {
		this.file_path = path;
	}

	writeLine(line) {
		let self = this
		fs.appendFile(this.file_path, line + '\n', function (err, file) {
			if (err) throw err;
			console.log(`File ${self.file_path} created and opened`);
			});
	}

	pos() {

	}

	rewind() {

	}

	close() {
		fs.closeFile(this.file_path);
	}
}

// Decorator
class WriterDecorator {
	constructor(real_writer) {
		this.real_writer = real_writer;
	}

	writeLine(line) {
		this.real_writer.writeLine(line);
	}

	close() {
		this.real_writer.close();
	}
}

// Component
class NumberingWriter extends WriterDecorator {
	constructor(real_writer) {
		super(real_writer);
		this.line_number = 1;
	}

	writeLine(line) {
		this.real_writer.writeLine(this.line_number + ': ' + line);
	}
}

// Component
class CheckSummingWriter extends WriterDecorator {
	constructor(real_writer) {
		this.check_sum = 0;
	}

	writeLine(line) {

	}
}

// Component
class TimeStampingWriter extends WriterDecorator {

	writeLine(line) {
		this.real_writer.writeLine(new Date() + ': ' + line);
	}
}

let writer = new TimeStampingWriter(new NumberingWriter(new SimpleWriter("final.txt")));
writer.writeLine('Hello Out There');