Validate whether members can share the SharePoint Site and its folders & files

spmemberscanshare.js

//getRequest method reference  
//https://gist.github.com/ktskumar/a9e9df497673e9fd26ead8532b9ff425  

//Modify domain.sharepoint.com with your SharePoint site URL
getRequest("https://domain.sharepoint.com/_api/web?$select=MembersCanShare").then(function(output) {  
    var result = JSON.parse(output.response);
    if (result.MembersCanShare){  
      alert("Members can share this site and its folder & files");  
    }else{  
      alert("Members do not have permission to share this site!");  
    }      
});

//Shantha Kumar T
//https://www.ktskumar.com