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util: fix deprecated class prototype #8105

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util: fix deprecated class prototype #8105

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util: fix deprecated class prototype 
Ensure the wrapped class prototype is exactly the unwrapped class
prototype, rather than an object whose prototype is the unwrapped
class prototype.

This ensures that instances of the unwrapped class are instances
of the wrapped class. This is useful when both a wrapped class and
a factory for the unwrapped class are both exposed.

Ref: #8103
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@bengl
bengl committed Aug 14, 2016
commit 651c92cad15c60e053ad71db49b3105f4372097c
5 changes: 4 additions & 1 deletion lib/internal/util.js
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Expand Up @@ -69,7 +69,10 @@ exports._deprecate = function(fn, msg) {
// The wrapper will keep the same prototype as fn to maintain prototype chain
Object.setPrototypeOf(deprecated, fn);
if (fn.prototype) {
Object.setPrototypeOf(deprecated.prototype, fn.prototype);
// Setting this (rather than using Object.setPrototype, as above) ensures
// that calling the unwrapped constructor gives an instanceof the wrapped
// constructor.
deprecated.prototype = fn.prototype;
}

return deprecated;
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3 changes: 3 additions & 0 deletions test/fixtures/deprecated-userland-class.js
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Expand Up @@ -7,6 +7,9 @@ class deprecatedClass {
const deprecated = util.deprecate(deprecatedClass, 'deprecatedClass is deprecated.');

const instance = new deprecated();
const deprecatedInstance = new deprecatedClass();

assert(instance instanceof deprecated);
assert(instance instanceof deprecatedClass);
assert(deprecatedInstance instanceof deprecated);
assert(deprecatedInstance instanceof deprecatedClass);