gecko/testing/mochitest/mozprefs.js

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(function() {
// NOTE: You *must* also include this line in any test that uses this file:
netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
var prefService = Components.classes["@mozilla.org/preferences-service;1"]
.getService(Components.interfaces.nsIPrefService);
function determinePrefKind(branch, prefName) {
switch (branch.getPrefType(prefName)) {
case branch.PREF_STRING: return "CharPref";
case branch.PREF_INT: return "IntPref";
case branch.PREF_BOOL: return "BoolPref";
default: /* PREF_INVALID */ return "ComplexValue";
}
}
function memoize(fn, obj) {
var cache = {}, sep = '___',
join = Array.prototype.join;
return function() {
var key = join.call(arguments, sep);
if (!(key in cache))
cache[key] = fn.apply(obj, arguments);
return cache[key];
};
}
var makeAccessor = memoize(function(pref) {
var splat = pref.split('.'),
basePref = splat.pop(),
branch, kind;
try {
branch = prefService.getBranch(splat.join('.') + '.')
} catch (e) {
alert("Calling prefService.getBranch failed: " +
"did you read the NOTE in mozprefs.js?");
throw e;
}
kind = determinePrefKind(branch, basePref);
return function(value) {
var oldValue = branch['get' + kind](basePref);
if (arguments.length > 0)
branch['set' + kind](basePref, value);
return oldValue;
};
});
/* function pref(name[, value[, fn[, obj]]])
* -----------------------------------------
* Use cases:
*
* 1. Get the value of the dom.disable_open_during_load preference:
*
* pref('dom.disable_open_during_load')
*
* 2. Set the preference to true, returning the old value:
*
* var oldValue = pref('dom.disable_open_during_load', true);
*
* 3. Set the value of the preference to true just for the duration
* of the specified function's execution:
*
* pref('dom.disable_open_during_load', true, function() {
* window.open(this.getUrl()); // fails if still loading
* }, this); // for convenience, allow binding
*
* Rationale: Unless a great deal of care is taken to catch all
* exceptions and restore original preference values,
* manually setting & restoring preferences can lead
* to unpredictable test behavior. The try-finally
* block below eliminates that risk.
*/
function pref(name, /*optional:*/ value, fn, obj) {
var acc = makeAccessor(name);
switch (arguments.length) {
case 1: return acc();
case 2: return acc(value);
default:
var oldValue = acc(value),
extra_args = [].slice.call(arguments, 4);
try { return fn.apply(obj, extra_args) }
finally { acc(oldValue) } // reset no matter what
}
};
window.pref = pref; // export
})();