> `Proxy` is powerful, but it's not as good as `Object.observe` would've > been for some very simple tasks. > > Every time I wish I could use `Proxy` in a simple way, there's always some > issue with it. For example: https://jsfiddle.net/trusktr/hwfontLc/17 >
Because you are doing it wrong. Proxies can *only* observe on the object that they're created for. By setting Foo.prototype to a proxy, you can only observe operations on Foo.prototype, not instances of Foo. What you really want is to have new Foo() return a Proxy... which is counter-intuitive, admittedly, because we're all taught that a constructor should never explicitly return a value. This problem has been solved, a few times, with the introduction of membranes in JavaScript. In that environment, you would start with Foo and wrap it in a membrane proxy. Then, in invoking new Foo(), the "construct" trap of that proxy would return another roxy automatically, probably using the same proxy handler but a different proxy target. If it's any consolation, proxies are in general very hard to work with. You're only scratching the surface here. I recently gave a talk at TC39 (the standards body for ECMAScript) on membranes. One key takeaway is that the overhead in dealing with membrane-oriented proxies really is better off left to a library built for that purpose. Tom van Cutsem is working on an article summarizing the current state of membranes. I'm not sure if he has approved its general release yet, so stay tuned... Alex Vincent Edmonds, WA (on vacation) -- "The first step in confirming there is a bug in someone else's work is confirming there are no bugs in your own." -- Alexander J. Vincent, June 30, 2001
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