javascript - Trouble understanding Node.js callbacks -


today first foray nodejs , particularly stumped trying understand way following piece of logic flows. logic follows:

request({ uri: db.createdbquery('identifier:abcd1234') },                     function(err, response, body) {                         response.should.have.status(200);                         var search = json.parse(body);                         search.response.numfound.should.equal(1);                         done();                     });         });

at higher level understand http request being made , function being called @ juncture taking response , doing it. trying understand proper order of calls , how binding of variables take place in above given logic. how compiler know how bind return values request anonymous function? basically, want gain understanding on how things work under hood snippet.

thanks

your question isnt specific node.js, feature of javascript.

basically calling request() defined function request(obj, callback)

internally, http request being called, , once completed, calls callback function pointer. 

function request(obj, callback){     //http request logic...     var err = request_logic_internal_function();     var response = ...     var body = ...       callback(err, response, body) }

your code can restructured :

var options = { uri: db.createdbquery('identifier:abcd1234') }; var request_callback = function(err, response, body) {                         response.should.have.status(200);                         var search = json.parse(body);                         search.response.numfound.should.equal(1);                         done();                     }; request(options, request_callback);

what you're doing sending in function pointer variable.


Comments

Post a Comment

Popular posts from this blog

jquery - Invalid Assignment Left-Hand Side -

i trying assign class tag via jquery, resulting in error through firebug says "invalid assignment left-hand side" on fourth line below. <cfoutput> $('.pngfix a').each(function(index) { var hreflink = $(this).attr("href"); if (hreflink.tolowercase() = '../audio.cfm') { $(this).addclass('audioimg'); } }); </cfoutput> looking around online, looks syntax problem, don't seem see it... any tips? thanks if (hreflink.tolowercase() = '../audio.cfm') that attempts assign value, rather check equality. change = operator == .
Read more

java - Play! framework 2.0: How to display multiple image? -

i need display gallery of photos. here template: @(photos: list[photo]) @title = { <bold>gallery</bold> } @main(title,"photo"){ <ul class="thumbnails"> @for(photo <- photos) { <li class="span3"> <a href="#" class="thumbnail"> <img src="@photo.path" alt=""> </a> </li> } </ul> } and here controller method: public static result getphotos() { return ok(views.html.photo.gallery.render(photo.get())); } and here photo bean : @entity public class photo extends model { @id public long id; @required public string label; public string path; public photo(string path, string label) { this.path = path; this.label = label; } private static finder<long, photo> find = new finder<long, photo>( long.class, photo.class); public static list<phot...
Read more

gmail - Is there any documentation for read-only access to the Google Contacts API? -

i want read-only access user's google contacts. there stackoverflow member wanted this, , received following answer : yes, there is, use https://www.googleapis.com/auth/contacts.readonly scope , "view contacts". this exchange reference read-only access google contacts can find using google. simply using access token obtained attempt read usual google contacts api (i.e. https://www.google.com/m8/feeds ) fails insufficient permissions. similarly, using google contacts api on new target fails 404 errors (for example https://www.googleapis.com/auth/contacts.readonly/default/full ). is there documentation anywhere on how use api, or permissible way access google contacts api full read-write access?
Read more