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91 lines
3.0 KiB
91 lines
3.0 KiB
/**
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* koSession offers observables whose values are tied to the browser session or history:
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*
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* sessionValue(key) - an observable preserved across history entries and reloads.
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*
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* Note: we could also support "browserValue", shared across all tabs and across browser restarts
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* (same as sessionValue but using window.localStorage), but it seems more appropriate to store
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* such values on the server.
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*/
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/* global window, $ */
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var _ = require('underscore');
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var ko = require('knockout');
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/**
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* Maps a string key to an observable. The space of keys is shared for all kinds of observables,
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* and they differ only in where they store their state. Each observable gets several extra
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* properties:
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* @property {String} ksKey The key used for storage. It should be unique across koSession values.
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* @property {Object} ksDefault The default value if the storage doesn't have one.
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* @property {Function} ksFetch The method to fetch the value from storage.
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* @property {Function} ksSave The method to save the value to storage.
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*/
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var _sessionValues = {};
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function createObservable(key, defaultValue, methods) {
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var obs = _sessionValues[key];
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if (!obs) {
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_sessionValues[key] = obs = ko.observable();
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obs.ksKey = key;
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obs.ksDefaultValue = defaultValue;
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obs.ksFetch = methods.fetch;
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obs.ksSave = methods.save;
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obs.dispose = methods.dispose;
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// We initialize the observable before setting rateLimit, to ensure that the initialization
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// doesn't end up triggering subscribers that are about to be added (which seems to be a bit
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// of a problem with rateLimit extender, and possibly deferred). This workaround relies on the
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// fact that the extender modifies its target without creating a new one.
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obs(obs.ksFetch());
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obs.extend({deferred: true});
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obs.subscribe(function(newValue) {
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if (newValue !== this.ksFetch()) {
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console.log("koSession: %s changed %s -> %s", this.ksKey, this.ksFetch(), newValue);
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this.ksSave(newValue);
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}
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}, obs);
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}
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return obs;
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}
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/**
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* Returns an observable whose value sticks across reloads and navigation, but is different for
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* different browser tabs. E.g. it may be used to reflect whether a side pane is open.
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* The `key` isn't visible to the user, so pick any unique string name.
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*/
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function sessionValue(key, optDefault) {
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return createObservable(key, optDefault, sessionValueMethods);
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}
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exports.sessionValue = sessionValue;
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var sessionValueMethods = {
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'fetch': function() {
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var value = window.sessionStorage.getItem(this.ksKey);
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if (!value) {
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return this.ksDefaultValue;
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}
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try {
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return JSON.parse(value);
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} catch (e) {
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return this.ksDefaultValue;
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}
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},
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'save': function(value) {
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window.sessionStorage.setItem(this.ksKey, JSON.stringify(value));
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},
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'dispose': function(value) {
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window.sessionStorage.removeItem(this.ksKey);
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}
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};
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function onApplyState() {
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_.each(_sessionValues, function(obs, key) {
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obs(obs.ksFetch());
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});
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}
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$(window).on('applyState', onApplyState);
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