Example to scale content to fit the current screen resolution with the option to recieve "width" and "height" from external or from browser's available client screen.

AppDelegate.js

/****************************************************************************
 Copyright (c) 2010-2012 cocos2d-x.org
 Copyright (c) 2008-2010 Ricardo Quesada
 Copyright (c) 2011      Zynga Inc.

 http://www.cocos2d-x.org

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 of this software and associated documentation files (the "Software"), to deal
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 copies of the Software, and to permit persons to whom the Software is
 furnished to do so, subject to the following conditions:

 The above copyright notice and this permission notice shall be included in
 all copies or substantial portions of the Software.

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 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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var cc = cc = cc || {};

/**
 @brief    The cocos2d Application.

 The reason for implement as private inheritance is to hide some interface call by CCDirector.
 */
cc.AppDelegate = cc.Application.extend({
    ctor:function () {
        this._super();
    },
    /**
     @brief    Implement for initialize OpenGL instance, set source path, etc...
     */
    initInstance:function () {
        return true;
    },

    /**
     @brief    Implement CCDirector and CCScene init code here.
     @return true    Initialize success, app continue.
     @return false   Initialize failed, app terminate.
     */
    applicationDidFinishLaunching:function () {
        // initialize director
        var pDirector = cc.Director.sharedDirector();

        // save the self pointer
        var selfPointer = this;
        // set the flag of finish loading
        global.isAppFinishedLoading = 1;
        
        // TODO: Insert the first time (one time) initialization here.
        // get winSize and set centerPos
        //winSize = cc.Director.sharedDirector().getWinSize();
        util.detectDevice();
        // calculate the global's scale factor based on whether it's fixed scaling, or automatically detect from device's screen
        if(global.isFixedScaling)
        {
            global.scale = util.getScaleFactorFromResolution(global.targetResolutionWidth, global.targetResolutionHeight);

            cc.canvas.width = cc.originalCanvasSize.width * global.scale;
            cc.canvas.height = cc.originalCanvasSize.height * global.scale;
            cc.renderContext.translate(0, cc.canvas.height);
            cc.renderContext.scale(global.scale, global.scale);
            cc.Director.sharedDirector().setContentScaleFactor(global.scale);
        }
        else
        {
            this.adjustSizeForWindow();
            window.addEventListener("resize", function (event) {
                selfPointer.adjustSizeForWindow();
            });
        }
        
        // get winSize (based on scaled resolution)
        // cache winSize and centerPos
        winSize = cc.Director.sharedDirector().getWinSize();
        centerPos = cc.ccp(winSize.width/2, winSize.height/2);
        
        util.log("baseResolution: " + global.baseResolutionWidth + ", " + global.baseResolutionHeight);
        util.log("targetResolutionWidth: " + global.targetResolutionWidth + ", " + global.targetResolutionHeight);
        util.log("winSize: " + winSize.width + ", " + winSize.height);
        util.log("centerPos: " +centerPos.x + ", " + centerPos.y);
        util.log("global.scale: " + global.scale);

        // enable High Resource Mode(2x, such as iphone4) and maintains low resource on other devices.
        // pDirector->enableRetinaDisplay(true);

        // show FPS
        if(global.isShowFPS)
            pDirector.setDisplayFPS(true);

        // pDirector->setDeviceOrientation(kCCDeviceOrientationLandscapeLeft);

        // set FPS. the default value is 1.0/60 if you don't call this
        pDirector.setAnimationInterval(1.0 / 60);

        // create a scene. it's an autorelease object
        var pScene = MainMenu.scene();
        
        // run
        pDirector.runWithScene(pScene);
        return true;
    },

    /**
     @brief  The function be called when the application enter background
     @param  the pointer of the application
     */
    applicationDidEnterBackground:function () {
        cc.Director.sharedDirector().pause();
    },

    /**
     @brief  The function be called when the application enter foreground
     @param  the pointer of the application
     */
    applicationWillEnterForeground:function () {
        cc.Director.sharedDirector().resume();
    },

    // Adjust size for the current window's resolution
    adjustSizeForWindow:function () {
        if(global.isIntegrateTest)
            global.scale = util.getScaleFactorFromResolution(contentWidth, contentHeight);
        else
            global.scale = util.getScaleFactorFromResolution(window.innerWidth, window.innerHeight);

        cc.canvas.width = cc.originalCanvasSize.width * global.scale;
        cc.canvas.height = cc.originalCanvasSize.height * global.scale;
        cc.renderContext.translate(0, cc.canvas.height);
        cc.renderContext.scale(global.scale, global.scale);
        cc.Director.sharedDirector().setContentScaleFactor(global.scale);
    }
});