1 | // Copyright 2017-2022 @polkadot/types authors & contributors
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2 | // SPDX-License-Identifier: Apache-2.0
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3 | import { isUndefined } from "./is/undefined.js";
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4 | export function lazyMethod(result, item, creator, getName) {
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5 | const name = getName ? getName(item) : item.toString();
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6 | let value;
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7 | Object.defineProperty(result, name, {
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8 | // This allows for re-configuration with the embedded defineProperty below
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9 | // and ensures that on tested browsers and Node, it _will_ be redefined
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10 | // and thus short-circuited for future access
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11 | configurable: true,
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12 | enumerable: true,
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13 | // Use a function here, we don't want to capture the outer this, i.e.
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14 | // don't use arrow functions in this context since we have a this inside
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15 | get: function () {
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16 | // This check should _always_ be false and unneeded, since we override
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17 | // with a value below ... however we ensure we are quire vigilant against
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18 | // all environment failures, so we are rather be safe than sorry
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19 | if (isUndefined(value)) {
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20 | value = creator(item);
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21 |
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22 | try {
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23 | // re-define the property as a value, next time around this
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24 | // getter will only return the computed value
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25 | Object.defineProperty(this, name, {
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26 | value
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27 | });
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28 | } catch {// ignore any errors, since this _should_ not happen due to
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29 | // the "configurable" property above. But if it ever does
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30 | // from here-on we will be the cached value the next time
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31 | // around (with a very slight dip in performance)
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32 | }
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33 | }
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34 |
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35 | return value;
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36 | }
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37 | });
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38 | }
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39 | export function lazyMethods(result, items, creator, getName) {
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40 | for (let i = 0; i < items.length; i++) {
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41 | lazyMethod(result, items[i], creator, getName);
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42 | }
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43 |
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44 | return result;
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45 | } |
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