javascript - In KnockoutJS, is there a specific order in which computed values must be declared? -


i javascript runtime error when run code below. uncaught typeerror: cannot read property 'name' of null in dep3 when accessing self.dep2().name.

the error goes away if move declaration of dep2 above of dep1. bug in knockout or i'm doing wrong? seems me dep3 being recomputed result of dep1 changing before dep2 has been recomputed have expected knockout able handle scenario.

function viewmodel () {     var self = this;      self.root = ko.observable(null);      self.dep1 = ko.computed(function () {         return self.root() ? self.root().prop1 : null;     });      self.dep2 = ko.computed(function () {         return self.root() ? self.root().prop2 : null;     });      self.dep3 = ko.computed(function () {         if (self.dep1()) {             return self.dep2().name;         }     }); }  globalviewmodel = new viewmodel();  globalviewmodel.root({     prop1: {name: "thisispropone"},     prop2: {name: "thisisproptwo"} });

you right way dependencies evaluated. change root trigger dep1 , dep2 re-evaluated, change dep1 triggers dep3 first.

in case, 1 option throttle dep3 like:

self.dep3 = ko.computed(function () {     if (self.dep1()) {         return self.dep2().name;     } }).extend({ throttle: 1 });

otherwise, checkout michael best's deferred updates plugin here: https://github.com/mbest/knockout-deferred-updates, handle in more robust way throttling.


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