javascript - Promise's second .then() not failing -

-

this question has answer here:

i'm having trouble chaining .then() calls promise. when executing following code:

var prom = new promise(function(resolve, reject) {   //let's fail   reject(error("buuuu!")); });  var thenable =  prom.then(     function(done) {         console.log("first handler: done!: argument: ", done);         return "first then: done";     },     function(fail) {         console.error("first handler: fail!. argument: ", fail);         return "first then: fail";     } ).then(     function(done) {         console.info("second handler: done!.  argument: ", done);     },     function(fail) {         console.error("second handler: fail!.  argument: ", fail);     } );

this prints following in console:

first handler: fail!. argument:  error {stack: (...), message: "buuuu!"} second handler: done!.  argument:  first then: fail


why second then() has done handler called instead of fail one?

is bug chrome? (note i'm interested in google chrome's behavior)

do need resort returning pre-resolved/rejected promises .then handlers?

why second then() has done handler called instead of fail one?

because handled error in first then() of chain already, making promise resolve "first then: fail" string returned it.

is bug chrome?

no, that's how promises supposed work.

do need resort returning pre-resolved/rejected promises .then handlers?

you can that, yes. other ways trigger second fail handler be:

  • simply omit first error handler:

    prom.then(function(done) {     console.log("first handler: done!: argument: ", done);     return "first then: done"; }).then(function(done) {     console.info("second handler: done!.  argument: ", done); }, function(fail) {     console.error("second handler: fail!.  argument: ", fail); });

  • or rethrow exception (that's similar returning rejected promise):

    prom.then(function(done) {     console.log("first handler: done!: argument: ", done);     return "first then: done"; }, function(fail) {     console.error("first handler: fail!. argument: ", fail);     throw new error("first then: fail"); // or: throw fail;     // alternatively, can return rejected promise:     return promise.reject(new error("first then: fail")); }).then(function(done) {     console.info("second handler: done!.  argument: ", done); }, function(fail) {     console.error("second handler: fail!.  argument: ", fail); });

Comments

Post a Comment

Popular posts from this blog

c++ - OpenCV Error: Assertion failed <scn == 3 ::scn == 4> in unknown function, -

-
i read alot other solution still confused should mine... #include <opencv2/objdetect/objdetect.hpp> #include <opencv2/highgui/highgui.hpp> #include <opencv2/imgproc/imgproc.hpp> #include <iostream> #include <stdio.h> using namespace std; using namespace cv; int main(int argc, const char** argv) { //create cascade classifier object used face detection cascadeclassifier face_cascade; //use haarcascade_frontalface_alt.xml library face_cascade.load("haarcascade_frontalface_alt.xml"); //setup video capture device , link first capture device videocapture capturedevice; capturedevice.open(0); //setup image files used in capture process mat captureframe; mat grayscaleframe; //create window present results namedwindow("outputcapture", 1); //create loop capture , find faces while (true) { //capture new image frame capturedevice >> captureframe; ...
Read more

php - render data via PDO::FETCH_FUNC vs loop -

-
i've been using 2 methods render data. the first one: function name($id,$name){ return '<div id="'.$id.'">'.$name.'</div>'; } echo implode($pdo->query("select id,name user")->fetchall(pdo::fetch_func,'name')); the second one: $users = $pdo->query("select id,name user")->fetchall(pdo::fetch_obj); foreach($users $user){ echo name($user->id,$user->name); } i don't understand how pdo::fetch_func works. tried figure out. however, not well-documented. could please explain fetch mode? , also, 1 performs better? thank you. both methods wrong , have learn how use templates , how separate business logic presentation logic. $users = $pdo->query("select id,name user")->fetchall(pdo::fetch_obj); tpl::assign('users', $users); is code business logic part. then in template <?php foreach $users $row): ?> <div id="<?=$...
Read more

The canvas has been tainted by cross-origin data in chrome only -

-
uncaught securityerror: failed execute 'getimagedata' on 'canvasrenderingcontext2d': canvas has been tainted cross-origin data i getting above error in chrome. code(following) works fine in mozilla. have not corss domain issue. why above error in chrome? var wheel_canvas, wheel_context, can_w, can_h, wheel_grd; var large_radius = 160; var small_radius = 120; var wheel_canvas = document.getelementbyid('wheel_canvas'); var wheel_context = wheel_canvas.getcontext('2d'); var can_w = $(wheel_canvas).width(); var can_h = $(wheel_canvas).height(); var centerx = can_w / 2, centery = can_h / 2; var wheel_grd = null; test('#ff0000'); function test(hex) { $('#clrpicker').css({'left': 210, 'top': 210 }); inverted = hexbw(hex); $('#color_val_show').val(hex); current_color_hex_val_selected = hex; $('#color_val_show').css({'color':inverted,'background':hex}); fillgradient...
Read more