What is _spPageContextInfo ?
_spPageContextInfo is a JavaScript context variable, which will rendered for each SharePoint page. _spPageContextInfo holds few proprieties which will be useful in JavaScript and client object model code. _ spPageContextInfo has below properties: webServerRelativeUrl webAbsoluteUrl siteAbsoluteUrl serverRequestPath layoutsUrl webTitle webTemplate tenantAppVersion isAppWeb webLogoUrl webLanguage currentLanguage currentUICultureName currentCultureName env nid fid clientServerTimeDelta updateFormDigestPageLoaded siteClientTag crossDomainPhotosEnabled webUIVersion webPermMasks pagePersonalizationScope userId userLoginName systemUserKey alertsEnabled siteServerRelativeUrl allowSilverlightPrompt themedCssFolderUrl themedImageFileNames To know properties of _spPageContextInfo, go to view page source and find text with "_spPageContextInfo".