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The `preferences/service` module provides access to the
application-wide preferences service singleton.

To define preferences for your own add-on and expose them to the user in
the [Add-on Manager](https://developer.mozilla.org/en-US/docs/Addons/Add-on_Manager),
you can use the [simple-prefs](modules/sdk/simple-prefs.html) module.

<api name="set">
@function
Sets the application preference `name` to `value`.
@param name {string} Preference name.
@param value {string,number,boolean} Preference value.

**Example:**

    var name = "extensions.checkCompatibility.nightly";
    require("sdk/preferences/service").set(name, false);
</api>


<api name="get">
@function
Gets the application preference `name`.
@param name {string}
@param defaultValue {string,number,boolean} Preference value.
@returns {string,number,boolean} Preference value, returns a default value if no
preference is set.

**Example:**

    var name = "extensions.checkCompatibility.nightly";
    var nightlyCompatChk = require("sdk/preferences/service").get(name);
</api>


<api name="has">
@function
@param name {string} Preference name.
@returns {boolean} Returns whether or not the application preference `name` exists.

**Example:**

    var name = "extensions.checkCompatibility.nightly";
    if (require("sdk/preferences/service").has(name)) {
      // ...
    }
</api>


<api name="keys">
@function
@param root {string} Preference root name.
@returns {array} Returns an array of strings representing the child preferences of the root of this branch.
</api>


<api name="isSet">
@function
@param name {string} Preference name.
@returns {boolean}
Returns whether or not the application preference `name` both exists
and has been set to a non-default value by the user (or a program
acting on the user's behalf).

**Example:**

    var name = "extensions.checkCompatibility.nightly";
    if (require("sdk/preferences/service").isSet(name)) {
      // ...
    }
</api>


<api name="reset">
@function
Clears a non-default, user-set value from the application preference
`name`. If no user-set value is defined on `name`, the function
does nothing. If no default value exists the preference will cease to exist.
@param name {string} Preference name.

**Example:**

    var name = "extensions.checkCompatibility.nightly";
    require("sdk/preferences/service").reset(name);
</api>

<api name="getLocalized">
@function
Gets the localized value for an application preference `name`.
@param name {string}
@param defaultValue {string} Preference value.
@returns {string} Localized preference value, returns a default value if no
preference is set. Some preferences refer to a properties file.
So that `prefs.get` returns the properties file URL whereas
`prefs.getLocalized` returns the value defined in the properties file.

**Example:**

    var prefs = require("sdk/preferences/service");
    var name = "general.useragent.locale";
    prefs.get(name); // is equal to "chrome://global/locale/intl.properties"
    prefs.getLocalized(name) // is equal to "en-US"

</api>

<api name="setLocalized">
@function
Sets the localized application preference `name` to `value`.
@param name {string} Preference name.
@param value {string} Preference value, a URL to a properties file

**Example:**

    require("sdk/preferences/service").set("general.useragent.locale",
                                       "chrome://global/locale/intl.properties");

</api>
