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Guarding Ember's computed properties

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[前端(javascript) 所属分类 前端(javascript) | 发布者 店小二05 | 时间 2016 | 作者 红领巾 ] 0人收藏点击收藏

Sometimes you hunt a bug that just won't show. It just literally won't allow itself to be found. Recently I've had one of those cases. This time it was just unimaginable what has actually happened. Someone, possibly by mistake, has overridden an Ember.ComputedProperty thus breaking the chain of updates. On top of that the app did updates to the model using websockets changing other properties of that model. This resulted in very strange flickering of values in an edit field. Very hard to diagnose.

After the bug was fixed I started looking at possible ways to guard it in the future and possibly to find other places where the same happens. There are 2 cases where this might happend:

using this.set('property', 'value'); using Handlebars template

One possible solution would be to reopen the Ember.Object class and to override the Ember.Object.set method. Unfortunately it only guards you from explicit calls to this.set(...) and all the overrides from Handlebars template remain silent.

But there is hope!

There is another class, Ember.ComputedProperty that is actually used as the tool to get and set computed properties. It also features a set method that can be monkey-patched to do our check:

(function() { var orgSet = Ember.ComputedProperty.prototype.set; Ember.ComputedProperty.prototype.set = function(obj, key) { if (obj[key] && obj[key]._getter && !obj[key]._setter) { console.error("Overriding computed property " + key + " on " + obj._debugContainerKey); } return orgSet.apply(this, arguments); }; })();

In this way if you override the computed property in a handlebars template or in the code you'll know about it. I only wish this would be part of the core framework. It would shave about 10 mandays of my project...

Here is an example project with the fix applied.

Have fun!

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