1 | var onceIdle = require('../once-idle')
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2 |
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3 | module.exports = function (update, onBind, onUnbind) {
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4 | var lazy = false
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5 | var context = this
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6 | var updating = false
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7 |
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8 | var obj = {
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9 | live: false,
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10 | nextTick: false,
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11 | idle: false,
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12 | suspended: false,
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13 | update: update,
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14 | value: null,
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15 | listeners: [],
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16 |
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17 | broadcast: function () {
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18 | if (obj.nextTick) {
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19 | if (!updating) {
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20 | updating = true
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21 | setImmediate(broadcast)
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22 | }
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23 | } else {
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24 | broadcast()
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25 | }
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26 | },
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27 |
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28 | transaction: function (value, cb) {
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29 | var originalValue = obj.suspended
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30 | obj.suspended = true
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31 | cb(value)
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32 | obj.suspended = originalValue
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33 | obj.broadcast()
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34 | },
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35 |
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36 | onUpdate: function () {
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37 | if (obj.idle) {
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38 | if (!updating) {
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39 | updating = true
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40 | onceIdle(obj.updateAndBroadcast)
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41 | }
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42 | } else if (obj.nextTick) {
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43 | if (!updating) {
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44 | updating = true
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45 | setImmediate(obj.updateAndBroadcast)
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46 | }
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47 | } else {
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48 | obj.updateAndBroadcast()
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49 | }
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50 | },
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51 |
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52 | updateAndBroadcast: function () {
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53 | updating = false
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54 | if (update.call(context)) {
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55 | broadcast()
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56 | }
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57 | },
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58 |
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59 | checkUpdated: function () {
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60 | if (!obj.live || lazy || updating) {
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61 | lazy = false
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62 | if (obj.nextTick && obj.live && lazy) {
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63 | obj.onUpdate()
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64 | } else {
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65 | update.apply(context)
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66 | }
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67 | }
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68 | },
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69 |
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70 | getValue: function () {
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71 | obj.checkUpdated.apply(context)
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72 | return obj.value
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73 | },
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74 |
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75 | addListener: function (listener) {
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76 | if (typeof listener !== 'function') {
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77 | throw new Error('Listeners must be functions.')
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78 | }
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79 |
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80 | obj.listeners.push(listener)
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81 |
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82 | if (!obj.live) {
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83 | obj.live = true
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84 | lazy = true
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85 | onBind.apply(context)
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86 | }
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87 |
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88 | return function release () {
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89 | for (var i = 0, len = obj.listeners.length; i < len; i++) {
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90 | if (obj.listeners[i] === listener) {
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91 | obj.listeners.splice(i, 1)
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92 | break
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93 | }
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94 | }
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95 | if (!obj.listeners.length && obj.live) {
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96 | obj.live = false
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97 | onUnbind.apply(context)
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98 | }
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99 | }
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100 | }
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101 | }
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102 |
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103 | return obj
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104 |
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105 |
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106 |
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107 | function broadcast () {
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108 | if (!obj.suspended) {
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109 | var cachedListeners = obj.listeners.slice(0)
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110 | for (var i = 0, len = cachedListeners.length; i < len; i++) {
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111 | cachedListeners[i](obj.value)
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112 | }
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113 | }
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114 | }
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115 | }
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