You-dont-know-js: this & object prototypes - chapter 2 - example code seems wrong
When I run the code below:
function foo() {
console.log(this.a);
}
var a = 2;
foo(); // 2
I get "undefined" in my console but the book says it should print 2.
Where is the problem?
MostafaNasiri
All 12 comments
I dunno... works for me:
getify
on 30 Sep 2017
Weird! When I run this code in chrome's web console it gives me the correct output but when I run it with nodejs compiler then I get "undefined" instead of 2!
MostafaNasiri
on 30 Sep 2017
Node's "global scope" is not a purely standard JS environment and cannot be trusted to give you accurate JS behavior like this.
getify
on 30 Sep 2017
CommonJS wraps .js files in a boilerplate function. See https://nodejs.org/api/modules.html#modules_the_module_wrapper
bmeck
on 30 Sep 2017
I didn't know that. Thanks guys!
MostafaNasiri
on 30 Sep 2017
@bmeck on that topic, I've always wondered why Node has to do that for the main .js file it's executing, as opposed to only doing it for any modules you load?
getify
on 30 Sep 2017
@getify to inject things like require (scoped to file path and not a global) and module (process.mainModule === module) for people to use. Also prevents various differences like allowing top level return depending on how a module is loaded.
Node is also deciding to register this file type as a separate MIME : https://github.com/nodejs/TSC/issues/371
bmeck
on 30 Sep 2017
@bmeck doesn't node care that their deviations confuse JS devs? :)
IIRC the v8 API provides a way to inject identifiers into scope without having to wrap code in an IIFE, no?
getify
on 30 Sep 2017
@getify doesn't have files be wrapped/not wrapped depending on how they are loaded just add to the confusion?
bmeck
on 30 Sep 2017
it should be noted that injecting variables isn't sufficient, grammar/this value also changes
bmeck
on 30 Sep 2017
grammar/this should never have been changed, that's my point, it perpetually confuses developers, like in this thread.
getify
on 1 Oct 2017
That ship has long since passed and I was just explaining things.
On Sep 30, 2017 10:39 PM, "Kyle Simpson" notifications@github.com wrote:
grammar/this should never have been changed, that's my point, it
perpetually confuses developers, like in this thread.—
You are receiving this because you were mentioned.
Reply to this email directly, view it on GitHub
https://github.com/getify/You-Dont-Know-JS/issues/1156#issuecomment-333351074,
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bmeck
on 1 Oct 2017
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Most helpful comment
CommonJS wraps
.jsfiles in a boilerplate function. See https://nodejs.org/api/modules.html#modules_the_module_wrapper