gecko/toolkit/devtools/DevToolsUtils.js

240 lines
6.4 KiB
JavaScript

/* 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);
}
}
}
/**
* Interleaves two arrays element by element, returning the combined array, like
* a zip. In the case of arrays with different sizes, undefined values will be
* interleaved at the end along with the extra values of the larger array.
*
* @param Array a
* @param Array b
* @returns Array
* The combined array, in the form [a1, b1, a2, b2, ...]
*/
this.zip = function zip(a, b) {
if (!b) {
return a;
}
if (!a) {
return b;
}
const pairs = [];
for (let i = 0, aLength = a.length, bLength = b.length;
i < aLength || i < bLength;
i++) {
pairs.push([a[i], b[i]]);
}
return pairs;
};
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;
}
});
}
/**
* Safely get the property value from a Debugger.Object for a given key. Walks
* the prototype chain until the property is found.
*
* @param Debugger.Object aObject
* The Debugger.Object to get the value from.
* @param String aKey
* The key to look for.
* @return Any
*/
this.getProperty = function getProperty(aObj, aKey) {
let root = aObj;
try {
do {
const desc = aObj.getOwnPropertyDescriptor(aKey);
if (desc) {
if ("value" in desc) {
return desc.value;
}
// Call the getter if it's safe.
return hasSafeGetter(desc) ? desc.get.call(root).return : undefined;
}
aObj = aObj.proto;
} while (aObj);
} catch (e) {
// If anything goes wrong report the error and return undefined.
reportException("getProperty", e);
}
return undefined;
};
/**
* Determines if a descriptor has a getter which doesn't call into JavaScript.
*
* @param Object aDesc
* The descriptor to check for a safe getter.
* @return Boolean
* Whether a safe getter was found.
*/
this.hasSafeGetter = function hasSafeGetter(aDesc) {
let fn = aDesc.get;
return fn && fn.callable && fn.class == "Function" && fn.script === undefined;
};