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August 29, 2015 14:19
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Definitely Maybe with Proxy
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| const unwrapSymbol = Symbol(); | |
| function Definitely(x) { | |
| if (x == null || !(unwrapSymbol in x)) | |
| return x; | |
| return x[unwrapSymbol]; | |
| } | |
| const Nothing = new Proxy(Object.seal(function() {}), { | |
| get(target, key) { return key === unwrapSymbol ? void 0 : Nothing }, | |
| set() {}, | |
| has() { return true }, | |
| apply() { return Nothing }, | |
| construct() { return Nothing }, | |
| }); | |
| const maybeHandler = { | |
| get(target, key) { return key === unwrapSymbol ? target : Maybe(target[key]) }, | |
| has(target, key) { return key === unwrapSymbol || key in target }, | |
| apply(target, thisArg, argumentList) { | |
| if (thisArg !== Nothing) | |
| thisArg = Definitely(thisArg); | |
| return Maybe(target.apply(thisArg, argumentList)); | |
| }, | |
| }; | |
| function Maybe(x) { | |
| return x === Nothing || x == null ? Nothing : new Proxy(Object(x), maybeHandler); | |
| } | |
| // alert(Definitely(Maybe(self).document.scripts[0].parentNode.nodeName)) | |
| // alert(Definitely(Maybe(self).document.querySelectorAll("div").length)) |
Also I get this error (using Firefox):
>>> Maybe(self).document.querySelectorAll("foo")
TypeError: 'querySelectorAll' called on an object that does not implement interface Document.I don't know if there is anything to do to prevent this error?
Ah yes. We can't use the "thisArg" supplied to the apply hook in that case, because a Proxy won't work there. Instead, we just call Definitely on the "thisArg" to unwrap it first. Should work now : )
For Nothing's "has" hook, I was thinking that it "has" everything, with the value of all properties being Nothing.
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That's neat. Why do you return
trueline 15 (has() { return true },)? Because("foo" in Maybe(null)) === truesounds weird to me.Florent