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on this file since fa375fe was 6a3a178, checked in by Ema <ema_spirova@…>, 3 years ago |
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1 | export default function symbolObservablePonyfill(root) {
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2 | var result;
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3 | var Symbol = root.Symbol;
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4 |
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5 | if (typeof Symbol === 'function') {
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6 | if (Symbol.observable) {
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7 | result = Symbol.observable;
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8 | } else {
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9 |
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10 | if (typeof Symbol.for === 'function') {
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11 | // This just needs to be something that won't trample other user's Symbol.for use
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12 | // It also will guide people to the source of their issues, if this is problematic.
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13 | // META: It's a resource locator!
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14 | result = Symbol.for('https://github.com/benlesh/symbol-observable');
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15 | } else {
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16 | // Symbol.for didn't exist! The best we can do at this point is a totally
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17 | // unique symbol. Note that the string argument here is a descriptor, not
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18 | // an identifier. This symbol is unique.
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19 | result = Symbol('https://github.com/benlesh/symbol-observable');
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20 | }
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21 | try {
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22 | Symbol.observable = result;
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23 | } catch (err) {
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24 | // Do nothing. In some environments, users have frozen `Symbol` for security reasons,
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25 | // if it is frozen assigning to it will throw. In this case, we don't care, because
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26 | // they will need to use the returned value from the ponyfill.
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27 | }
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28 | }
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29 | } else {
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30 | result = '@@observable';
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31 | }
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32 |
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33 | return result;
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34 | };
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