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18 | let readyMap, queueMap;
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19 |
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20 | function isContentReady(element) {
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21 | if (element.childNodes.length > 0) {
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22 | setContentReady(element);
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23 | }
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24 | return readyMap.has(element);
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25 | }
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26 |
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27 | function setContentReady(element) {
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28 | readyMap.set(element, true);
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29 | }
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30 |
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31 | function addCallback(element, fn) {
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32 | if (!queueMap.has(element)) {
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33 | queueMap.set(element, []);
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34 | }
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35 | queueMap.get(element).push(fn);
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36 | }
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37 |
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38 | function consumeQueue(element) {
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39 | const callbacks = queueMap.get(element, []) || [];
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40 | queueMap.delete(element);
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41 | callbacks.forEach(callback => callback());
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42 | }
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43 |
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44 | export default function contentReady(element, fn = () => {}) {
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45 | if (readyMap === undefined) {
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46 | readyMap = new WeakMap();
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47 | queueMap = new WeakMap();
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48 | }
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49 |
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50 | addCallback(element, fn);
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51 |
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52 | if (isContentReady(element)) {
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53 | consumeQueue(element);
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54 | return;
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55 | }
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56 |
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57 | const observer = new MutationObserver(changes => {
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58 | setContentReady(element);
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59 | consumeQueue(element);
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60 | });
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61 | observer.observe(element, {childList: true, characterData: true});
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62 |
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63 |
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64 | setImmediate(() => {
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65 | setContentReady(element);
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66 | consumeQueue(element);
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67 | });
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68 | }
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