REST API to Delete folder from document library

Hope you have idea how to create SharePoint App.
If you are using NAPA tool then replace below codes in APP.js file.
So i am just focusing on the REST script part to do the activities

I recommend to go through REST API for SP document libraries before proceed.

HTML file in Default.aspx 
<div>
    <p>
        <b>Create Folder</b>
        <br />
        <input type="text" value="List Name Here" id=" DeleteFolder " />
        <button id="btnclick"> Delete Folder </button>
    </p>
</div>
----------------------
JS script in app.js (Paste the below methods in app.js file) Refer here
-----------------------
function FolderCreation()
{
    var executor;
 var getfoldername= document.getElementById("DeleteFolder").value;
    // Initialize the RequestExecutor with the app web URL.
    executor = new SP.RequestExecutor(appweburl);
    executor.executeAsync({
   url: appweburl + "/_api/SP.AppContextSite(@target)/web/GetFolderByServerRelativeUrl('lib/Folder B')?@target='" + hostweburl + "'",
        method: "POST",
}        
          headers:  
            {
              "X-HTTP-Method":"DELETE"  
            },  
success: FoldersSuccessHandler,
        error: FoldersErrorHandler
    });
}  
//Populate the selectFolders control after retrieving all of the folders.
function FoldersSuccessHandler(data) {
    alert("Folder Deleted successfully in Library");
}  
function FoldersErrorHandler(data, errorCode, errorMessage) {
    alert("Could not Delete a Folder in  Library: " + errorMessage);
}
//Utilities
// Retrieve a query string value.
// For production purposes you may want to use a library to handle the query string.
function getQueryStringParameter(paramToRetrieve) {
    var params = document.URL.split("?")[1].split("&");
    for (var i = 0; i < params.length; i = i + 1) {
        var singleParam = params[i].split("=");
        if (singleParam[0] == paramToRetrieve) return singleParam[1];
    }
}