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15 | export const mixin = (behaviour, sharedBehaviour = {}) => {
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16 | const instanceKeys = Reflect.ownKeys(behaviour);
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17 | const sharedKeys = Reflect.ownKeys(sharedBehaviour);
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18 | const typeTag = Symbol("isa");
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19 | function _mixin(clazz) {
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20 | for (let key of instanceKeys) {
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21 | const existing = Object.getOwnPropertyDescriptor(clazz.prototype, key);
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22 | if (!existing || existing.configurable) {
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23 | Object.defineProperty(clazz.prototype, key, {
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24 | value: behaviour[key],
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25 | writable: true,
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26 | });
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27 | }
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28 | else {
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29 |
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30 | }
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31 | }
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32 | Object.defineProperty(clazz.prototype, typeTag, { value: true });
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33 | return clazz;
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34 | }
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35 | for (let key of sharedKeys) {
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36 | Object.defineProperty(_mixin, key, {
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37 | value: sharedBehaviour[key],
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38 | enumerable: sharedBehaviour.propertyIsEnumerable(key),
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39 | });
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40 | }
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41 | Object.defineProperty(_mixin, Symbol.hasInstance, {
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42 | value: (x) => !!x[typeTag],
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43 | });
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44 | return _mixin;
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45 | };
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