How JavaScript Collects Your Garbage

Transcript

1. How JavaScript Collects Your Garbage Rory Fitzpatrick EdinburghJS November 2014
2. What is Garbage Collection?
3. In computer science, garbage collection (GC) is a form of automatic memory management. The garbage collector, or just collector, attempts to reclaim garbage, or memory occupied by objects that are no longer in use by the program. http://en.wikipedia.org/wiki/Garbage_collection_(computer_science)
4. var foo = {hello: “EdinJS”}; foo = null; // Creates garbage
5. Mark and sweep
6. 1 1 1 1 1 1 1 1 1 1 1 1 1
7. Why do I care?
9. var foo = {hello: “EdinJS”}; var bar = foo; foo = null; bar = null;
10. function sayHello(data) { setTimeout(function() { console.log(data.hello); }, 1000); } ! var foo = {hello: “EdinJS”}; sayHello(foo); foo = null;
11. function sayHello(data) { setInterval(function() { console.log(data.hello); }, 1000); } ! var foo = {hello: “EdinJS”}; sayHello(foo); foo = null;
12. When does GC run?
13. Code
14. DOM leaks
15. var el = document.getElementById(‘myBtn’); var data = { el: el, msg: ‘hello’ }; ! el.addEventListener(‘click’, function() { alert(data.msg); }); ! // Some time later ! el.parentNode.removeChild(el); IE<8
16. delete is good delete myObj.someProperty; ! myObj.someProperty; -> undefined
17. Hidden classes var data = { foo: “bar” }; ! doSomething(data); delete data.foo;
18. delete is bad
19. Always use var
20. V8 is clever function sayHello(data) { console.log(data.hello); ! setInterval(function() { console.log(‘interval’); debugger; // console.log(data) -> undefined }, 1000); } ! var foo = {hello: “EdinJS”}; sayHello(foo); foo = null;
21. JavaScript engines are smart Performance is hard Humans are dumb
22. Questions / Corrections @roryf github.com/roryf rory@fanduel.com
23. I am an imposter I love to procrastinate I have a fear of failure