![Closures Inner functions have access to the outer function's variables, even after the outer function has completed var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; }; var test = digit_name(); // test is a function that takes a value var text = test(3); console.log("text = " + text);](https://image.slidesharecdn.com/camta-nodejs-111209025621-phpapp02/85/Node-js-CAMTA-Presentation-33-320.jpg)
![Closures Inner functions have access to the outer function's variables, even after the outer function has completed var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; }; var test = digit_name(); // test is a function that takes a value var text = test(3); console.log("text = " + text);](https://image.slidesharecdn.com/camta-nodejs-111209025621-phpapp02/85/Node-js-CAMTA-Presentation-34-320.jpg)
![Closures Could be rewritten to use a self-executing function as follows var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; } () ; // digit_name is the result of running the outer function, // so it's a function that takes a value var name = digit_name(3); // name will be 'three'](https://image.slidesharecdn.com/camta-nodejs-111209025621-phpapp02/85/Node-js-CAMTA-Presentation-35-320.jpg)
Node.js: CAMTA Presentation
- 1. MUMPS is dead? Rob Tweed M/Gateway Developments Ltd http://www.mgateway.com Twitter: @rtweed
- 4. What is Node.js? … so what does that mean?
- 6. What is Node.js? Node.js is a server-side JavaScript environment.
- 7. What is Node.js? Node.js is a server-side JavaScript environment. Node.js is a server-side JavaScript interpreter that allows us to handle and make requests via JavaScript: In a web or networked environment
- 8. Just Javascript Browsers Node.js server process Javascript Javascript Database
- 9. So instead of this: http/ https Persistent connections Browser Browser Browser Web Server (Apache/ IIS) CSP Caché CSP interface Caché CSP interface Your scripts Your data EWD CSP pages
- 10. You'd have something like this: Browser Browser Browser Cach é http/ https WebLink interface Cach é CSP interface Child_process connections EWD Runtime Your scripts Your data EWD routines Node.js process Javascript Web server & request/response Handling logic stdin/stdout GT.M or Cach é
- 11. What is Node.js?
- 12. V8 Node.js uses the Google V8 engine to provide the Javascript environment V8 is the engine in the Chrome browser V8 is very fast!
- 13. What is Node.js?
- 14. What is Node.js? Node.js is a server-side JavaScript environment that uses an asynchronous event-driven model .
- 15. What is Node.js? Node.js is a server-side JavaScript environment that uses an asynchronous event-driven model . No threads Node.js runs in a single process, handling all client requests Non-blocking I/O Can't wait for slow resources to respond Files, databases, etc Must not block the process or everyone waits
- 16. Asynchronous I/O & Javascript Javascript is an ideal language for this No I/O in a browser Access to remote resources is asynchronous The A in Ajax! Send a request for a resource and define a handler to deal with it when it arrives "Call-back function"
- 17. Asynchronous I/O & Javascript On the server, in Node.js: Make a request for I/O (file/ database) Define a call-back function Move on immediately When the I/O is complete: Call-back function is fired to handle it
- 18. Asynchronous I/O & Javascript Synchronous read from a file in MUMPS: set file = "mydata.txt" open file:"r" use file read buffer // do something with the buffer contents … . // then move on to the next task
- 19. Asynchronous I/O & Javascript Synchronous read from a file in MUMPS: set file = "mydata.txt" open file:"r" use file read buffer // do something with the buffer contents … .// at this point the thread is blocked … .// until the buffer contents are read from the file // then move on to the next task
- 20. Asynchronous I/O & Javascript The Asynchronous way in Javascript: var fs = require('fs'); fs.readFile('mydata.txt', function (err, buffer) { // Do something with the data in the buffer }); // Immediately execute the next statements // while it waits for I/O
- 21. What is Node.js?
- 22. Node.js Evented I/O Node.js is a single process running an event loop When an event occurs, fire a call-back function to handle it When no events are coming in, the Node.js process sits in a dormant state
- 23. Node.js process A Node.js process can handle many thousands of clients Provided none of them block Provided none of them do CPU-intensive processing
- 24. Node.js / Javascript: popularity Node.js is now the most followed project on Github, exceeding Ruby on Rails Javascript is now the most popular language in the world, based on a number of measures including number of Github projects
- 25. Significance for GT.M & Cach é Opportunity to use Javascript as a primary scripting language Global storage for Javascript JSON / Global mapping
- 26. Why Javascript? The world's most popular language The world's sexiest, coolest server-side environment Javascript's dynamic interpreted nature has many similarities to MUMPS
- 27. Why not MUMPS? Rightly or wrongly, the perception in the mainstream is that the MUMPS language is old-fashioned and inherently broken Daily WTF article: http://thedailywtf.com/Articles/A_Case_of_the_MUMPS.aspx Yet global storage has a great deal to offer as a NoSQL database technology Result: the benefits and advantages of global storage are ignored because modern developers will refuse to learn the language
- 28. Making Global Storage Attractive Make it accessible via the coolest, sexiest, most popular language on the planet Demonstrate that global storage is a great NoSQL technology "Universal NoSQL Engine" http://www.mgateway.com/docs/universalNoSQL.pdf
- 29. Downside of Node.js Asynchronous programming Callback hell! Deeply nested call-backs Complexity of logic Essential to understand closures 2 main types: Dependent Concurrent Care needed when using for loops to invoke logic that includes callbacks
- 30. Dependent callbacks myFunc1(inputs, function(error, results) { var value = results.value; // myFunc2 can't run until myFunc1 returns its results myFunc2(value, function(error, results) { var myResult = results.value; }); });
- 31. Concurrent callbacks var count = 0; myFunc1(inputs, function(error, results) { count++; if (count === 3) myFunc4(inputs); }); myFunc2(inputs, function(error, results) { count++; if (count === 3) myFunc4(inputs); }); myFunc3(inputs, function(error, results) { count++; if (count === 3) myFunc4(inputs); }); // myFunc isn't invoked until all 3 functions are complete // Uses the properties of closures to allow count to be incremented by // the callbacks in the three functions
- 32. Closures Inner functions have access to the outer function's variables, even after the outer function has completed
- 33. Closures Inner functions have access to the outer function's variables, even after the outer function has completed var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; }; var test = digit_name(); // test is a function that takes a value var text = test(3); console.log("text = " + text);
- 34. Closures Inner functions have access to the outer function's variables, even after the outer function has completed var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; }; var test = digit_name(); // test is a function that takes a value var text = test(3); console.log("text = " + text);
- 35. Closures Could be rewritten to use a self-executing function as follows var digit_name = function() { var names = ['zero', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine']; return function(n) { return names[n]; }; } () ; // digit_name is the result of running the outer function, // so it's a function that takes a value var name = digit_name(3); // name will be 'three'
- 36. Downside of Node.js Asynchronous programming Database access functions can't return a value Value is embedded inside the callback Can't chain database functions as objects: document.getElementById('x').parent.firstChild.tagName
- 37. Accessing globals from Node.js Cache & GT.M: https://github.com/robtweed/ewdGateway Complete webserver + gateway for EWD Also includes global access functions, eg: get set getJSON mFunction