gecko/toolkit/devtools/DevToolsUtils.js

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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
"use strict";
/* General utilities used throughout devtools. */
let { Promise: promise } = Components.utils.import("resource://gre/modules/commonjs/sdk/core/promise.js", {});
let { Services } = Components.utils.import("resource://gre/modules/Services.jsm", {});
/**
* Turn the error |aError| into a string, without fail.
*/
this.safeErrorString = function safeErrorString(aError) {
try {
let errorString = aError.toString();
if (typeof errorString === "string") {
// Attempt to attach a stack to |errorString|. If it throws an error, or
// isn't a string, don't use it.
try {
if (aError.stack) {
let stack = aError.stack.toString();
if (typeof stack === "string") {
errorString += "\nStack: " + stack;
}
}
} catch (ee) { }
return errorString;
}
} catch (ee) { }
return "<failed trying to find error description>";
}
/**
* Report that |aWho| threw an exception, |aException|.
*/
this.reportException = function reportException(aWho, aException) {
let msg = aWho + " threw an exception: " + safeErrorString(aException);
dump(msg + "\n");
if (Components.utils.reportError) {
/*
* Note that the xpcshell test harness registers an observer for
* console messages, so when we're running tests, this will cause
* the test to quit.
*/
Components.utils.reportError(msg);
}
}
/**
* Given a handler function that may throw, return an infallible handler
* function that calls the fallible handler, and logs any exceptions it
* throws.
*
* @param aHandler function
* A handler function, which may throw.
* @param aName string
* A name for aHandler, for use in error messages. If omitted, we use
* aHandler.name.
*
* (SpiderMonkey does generate good names for anonymous functions, but we
* don't have a way to get at them from JavaScript at the moment.)
*/
this.makeInfallible = function makeInfallible(aHandler, aName) {
if (!aName)
aName = aHandler.name;
return function (/* arguments */) {
try {
return aHandler.apply(this, arguments);
} catch (ex) {
let who = "Handler function";
if (aName) {
who += " " + aName;
}
reportException(who, ex);
}
}
}
const executeSoon = aFn => {
Services.tm.mainThread.dispatch({
run: this.makeInfallible(aFn)
}, Components.interfaces.nsIThread.DISPATCH_NORMAL);
}
/**
* Like Array.prototype.forEach, but doesn't cause jankiness when iterating over
* very large arrays by yielding to the browser and continuing execution on the
* next tick.
*
* @param Array aArray
* The array being iterated over.
* @param Function aFn
* The function called on each item in the array.
* @returns Promise
* A promise that is resolved once the whole array has been iterated
* over.
*/
this.yieldingEach = function yieldingEach(aArray, aFn) {
const deferred = promise.defer();
let i = 0;
let len = aArray.length;
(function loop() {
const start = Date.now();
while (i < len) {
// Don't block the main thread for longer than 16 ms at a time. To
// maintain 60fps, you have to render every frame in at least 16ms; we
// aren't including time spent in non-JS here, but this is Good
// Enough(tm).
if (Date.now() - start > 16) {
executeSoon(loop);
return;
}
try {
aFn(aArray[i++]);
} catch (e) {
deferred.reject(e);
return;
}
}
deferred.resolve();
}());
return deferred.promise;
}
/**
* Like XPCOMUtils.defineLazyGetter, but with a |this| sensitive getter that
* allows the lazy getter to be defined on a prototype and work correctly with
* instances.
*
* @param Object aObject
* The prototype object to define the lazy getter on.
* @param String aKey
* The key to define the lazy getter on.
* @param Function aCallback
* The callback that will be called to determine the value. Will be
* called with the |this| value of the current instance.
*/
this.defineLazyPrototypeGetter =
function defineLazyPrototypeGetter(aObject, aKey, aCallback) {
Object.defineProperty(aObject, aKey, {
configurable: true,
get: function() {
const value = aCallback.call(this);
Object.defineProperty(this, aKey, {
configurable: true,
writable: true,
value: value
});
return value;
}
});
}