How to find the main window from your custom page

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/**
* @desc returns the window with the relativity context
* @returns {Object} the window with the relativity context
*/
function getRelativityPageBaseWindow() {
    /**
    * @const {Array<string>} Collection of supported properties expected to be on the window object.
    */
    const RELATIVITY_NAMESPACE_AND_SUPPORTED_PROPS = [
        "relativity",
        "relativity.config",
        "relativity.internal",
        "relativity.navigation"
    ];
    
    /**
    * @desc checks that the provided window object has the given properties on it
    * @param {Array<String>} props the Array of property names
    * @param {Object} winObj the window Object
    * @returns {Object} the window with the given properties
    */
    function findWindowByPropertiesInHierarchy(props, winObj) {
        let win = winObj;
        while (continueHierarchyCheck(props, win)) {
            win = win.opener || win; // win.opener is done before parent because opener will be falsy (null) on windows where window.parent !== window

            if (!ensureProps(win, props)) {
                win = win.parent || false; // save vs malformation
            }
        }
        return (!!win && ensureProps(win, props)) ? win : {};
    }
    
    /**
    * @desc checks whether we have to continue hierarchy check for given properties.
    * @param {Array<String>} props the Array of property names.
    * @param {Object} win the window Object
    * @returns {Boolean} returns a boolean value.
    */
    function continueHierarchyCheck(props, win) {
        return !!win && !(ensureProps(win, props) || (win === win.parent && !win.opener));
    }
    
    /**
    * @desc This function checks whether the given object has the given properties
    * @param {Object} obj the Object to evaluate
    * @param {Array} propNames the Array to evaluate against obj
    * @returns {Boolean} if the given properties are found
    */
    function ensureProps(obj, propNames) {
        try {
            return !!obj &&
                Array.isArray(propNames) &&
                propNames.every((prop) => checkProperty(obj, prop));
        } catch (e) {
            return e && false;
        }
    }
    
    /**
    * @desc This function checks whether the given object has the given property
    * @param {Object} obj the Object to evaluate
    * @param {String} prop the property to evaluate against obj
    * @returns {Boolean} if the given property is found
    */
    function checkProperty(obj, prop) {
        const propsAsArray = prop.split(".");
        return !!propsAsArray.reduce((prev, curr) => prev && prev[curr] || (typeof prev === "object" && prev.hasOwnProperty(curr)), obj);
    }
    
    return findWindowByPropertiesInHierarchy(RELATIVITY_NAMESPACE_AND_SUPPORTED_PROPS, window);
}