diff options
author | Rogan Creswick <creswick@galois.com> | 2012-03-30 17:07:02 -0700 |
---|---|---|
committer | Rogan Creswick <creswick@galois.com> | 2012-03-30 17:07:02 -0700 |
commit | f6ab6622aab00fe7c2f4c3dc41f786ebbe0f0d73 (patch) | |
tree | 870111038542cd27153e1396ebdc063573249689 /tools/addon-sdk-1.4/packages/addon-kit/docs/simple-storage.md |
initial revision
Diffstat (limited to 'tools/addon-sdk-1.4/packages/addon-kit/docs/simple-storage.md')
-rw-r--r-- | tools/addon-sdk-1.4/packages/addon-kit/docs/simple-storage.md | 125 |
1 files changed, 125 insertions, 0 deletions
diff --git a/tools/addon-sdk-1.4/packages/addon-kit/docs/simple-storage.md b/tools/addon-sdk-1.4/packages/addon-kit/docs/simple-storage.md new file mode 100644 index 0000000..e34e333 --- /dev/null +++ b/tools/addon-sdk-1.4/packages/addon-kit/docs/simple-storage.md @@ -0,0 +1,125 @@ +The `simple-storage` module lets you easily and persistently store data across +application restarts. If you're familiar with [DOM storage][] on the Web, it's +kind of like that, but for add-ons. + +[DOM storage]: https://developer.mozilla.org/en/DOM/Storage + + +Introduction +------------ + +The simple storage module exports an object called `storage` that is persistent +and private to your add-on. It's a normal JavaScript object, and you can treat +it as you would any other. + +To store a value, just assign it to a property on `storage`: + + var ss = require("simple-storage"); + ss.storage.myArray = [1, 1, 2, 3, 5, 8, 13]; + ss.storage.myBoolean = true; + ss.storage.myNull = null; + ss.storage.myNumber = 3.1337; + ss.storage.myObject = { a: "foo", b: { c: true }, d: null }; + ss.storage.myString = "O frabjous day!"; + +You can store array, boolean, number, object, null, and string values. If you'd +like to store other types of values, you'll first have to convert them to +strings or another one of these types. + +Be careful to set properties on the `storage` object and not the module itself: + + // This is no good! + var ss = require("simple-storage"); + ss.foo = "I will not be saved! :("; + + +Quotas +------ + +The simple storage available to your add-on is limited. Currently this limit is +about five megabytes (5,242,880 bytes). You can choose to be notified when you +go over quota, and you should respond by reducing the amount of data in storage. +If the user quits the application while you are over quota, all data stored +since the last time you were under quota will not be persisted. You should not +let that happen. + +To listen for quota notifications, register a listener for the `"OverQuota"` +event. It will be called when your storage goes over quota. + + function myOnOverQuotaListener() { + console.log("Uh oh."); + } + ss.on("OverQuota", myOnOverQuotaListener); + +Listeners can also be removed: + + ss.removeListener("OverQuota", myOnOverQuotaListener); + +To find out how much of your quota you're using, check the module's `quotaUsage` +property. It indicates the percentage of quota your storage occupies. If +you're within your quota, it's a number from 0 to 1, inclusive, and if you're +over, it's a number greater than 1. + +Therefore, when you're notified that you're over quota, respond by removing +storage until your `quotaUsage` is less than or equal to 1. Which particular +data you remove is up to you. For example: + + ss.storage.myList = [ /* some long array */ ]; + ss.on("OverQuota", function () { + while (ss.quotaUsage > 1) + ss.storage.myList.pop(); + }); + + +Private Browsing +---------------- + +*This section applies only to add-ons running on Firefox.* + +If your storage is related to your users' Web history, personal information, or +other sensitive data, your add-on should respect [private browsing mode][SUMO]. +While private browsing mode is active, you should not store any sensitive data. + +Because any kind of data can be placed into simple storage, support for private +browsing is not built into the module. Instead, use the +[`private-browsing`](packages/addon-kit/docs/private-browsing.html) module to +check private browsing status and respond accordingly. + +For example, the URLs your users visit should not be stored during private +browsing. If your add-on records the URL of the selected tab, here's how you +might handle that: + + ss.storage.history = []; + var privateBrowsing = require("private-browsing"); + if (!privateBrowsing.active) { + var url = getSelectedTabURL(); + ss.storage.history.push(url); + } + +For more information on supporting private browsing, see its [Mozilla Developer +Network documentation][MDN]. While that page does not apply specifically to +SDK-based add-ons (and its code samples don't apply at all), you should follow +its guidance on best practices and policies. + +[SUMO]: http://support.mozilla.com/en-US/kb/Private+Browsing +[MDN]: https://developer.mozilla.org/En/Supporting_private_browsing_mode + + +<api name="storage"> +@property {object} + A persistent object private to your add-on. Properties with array, boolean, + number, object, null, and string values will be persisted. +</api> + +<api name="quotaUsage"> +@property {number} + A number in the range [0, Infinity) that indicates the percentage of quota + occupied by storage. A value in the range [0, 1] indicates that the storage + is within quota. A value greater than 1 indicates that the storage exceeds + quota. +</api> + +<api name="OverQuota"> +@event +The module emits this event when your add-on's storage goes over its quota. +</api> |