REST APIs to play with SharePoint Groups

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

Source Code in JS file:
Here we can call different methods from html button click as per need to perform action.
------------------------------------------------------------------------------------------------------------------------
    'use strict';
     
    var hostweburl;
    var appweburl;
 
    $(document).ready(function ()
    {
        //Get the URI decoded URLs.
        hostweburl = decodeURIComponent(getQueryStringParameter("SPHostUrl"));
        appweburl = decodeURIComponent(getQueryStringParameter("SPAppWebUrl"));
     
        // Load the js file and continue to load the page with information about the folders.
        // SP.RequestExecutor.js to make cross-domain requests
        $.getScript(hostweburl + "/_layouts/15/SP.RequestExecutor.js",creategroup);
    });
//--------------- ----------------------
     
    //Create Group
    function creategroup()
    {
        var executor;
         // Initialize the RequestExecutor with the app web URL.
        executor = new SP.RequestExecutor(appweburl);
     
        executor.executeAsync({
      url: appweburl + "/_api/SP.AppContextSite(@target)/web/sitegroups?@target= '" + hostweburl + "'",  
            method: "POST",
      body: “{'__metadata':{ 'type': 'SP.Group' }, 'Title':'New Group'}”,
            headers:  
            {  
                "content-type": "application/json; odata=verbose"
            },  
            success: function(data)  
            {  
                alert("Group CREATED SUCCESSFULLY ");  
            },  
            error: function(err)  
            {  
                alert("error: " + JSON.stringify(err));  
            }      });
    }
//--------------- ----------------------     

//Retrieve Groups
function retrivegroup()
{
    var executor;
    // Initialize the RequestExecutor with the app web URL.  
    executor = new SP.RequestExecutor(appweburl);
    executor.executeAsync({
        url: appweburl + "/_api/SP.AppContextSite(@target)/web/sitegroups?@target= '" + hostweburl + "'",
        method: "GET",
        headers: {
            "Accept": "application/json; odata=verbose"
        },
        success: getGroupsSuccessHandler,
        error: function(err) {
            alert("error: " + JSON.stringify(err));
        }
    });
}

function getGroupsSuccessHandler(data)
{
    var jsonObject = JSON.parse(data.body);
    var Groups = document.getElementById("RetriveGroups");
    if (Groups.hasChildNodes())
    {
        while (Groups.childNodes.length >= 1)
        {
            Groups.removeChild(Groups.firstChild);
        }
    }
    var results = jsonObject.d.results;
    for (var i = 0; i < results.length; i++)
    {
        var allgroups = document.createElement("option");
        allgroups.value = results[i].Title;
        allgroups.innerText = results[i].Title;
        Groups.appendChild(allgroups);
    }
}
//--------------- ----------------------

//Delete Users in groups
function DeleteUser()
{
    var executor;
    var userEmail = "gowthamdev@Gauti.onmicrosoft.com";
    // Initialize the RequestExecutor with the app web URL.
    executor = new SP.RequestExecutor(appweburl);
    executor.executeAsync({
        url: appweburl + "/_api/SP.AppContextSite(@target)/web/sitegroups(6)/users/getbyemail('" + userEmail + "')?@target='" + hostweburl + "'",
        method: "POST",
        headers: {
            "X-HTTP-Method": "DELETE"
        },
        success: function(data) {
            alert("User Deleted successfully in SharePoint Group");
        },
        error: function(err) {
            alert("error: " + JSON.stringify(err));
        }
    });
}
//--------------- ----------------------

//GetUsers in group
function getuser()
{
    var executor;
    var userEmail = "gowthamdev@Gauti.onmicrosoft.com";
    // Initialize the RequestExecutor with the app web URL.
    executor = new SP.RequestExecutor(appweburl);
    executor.executeAsync({
        url: appweburl + "/_api/SP.AppContextSite(@target)/web/sitegroups(6)/users?@target='" + hostweburl + "'",
        method: "GET",
        headers: {
            "Accept": "application/json; odata=verbose"
        },
        success: getUsersFromGroupSuccess,
        error: getUsersFromGroupError
    });
}
//Populate the selectUsers control after retrieving all of the users from group.
function getUsersFromGroupSuccess(data)
{
    var jsonObject = JSON.parse(data.body);
    var RetriveUsers = document.getElementById("RetriveUsers");
    if (RetriveUsers.hasChildNodes())
    {
        while (RetriveUsers.childNodes.length >= 1)
        {
            RetriveUsers.removeChild(RetriveUsers.firstChild);
        }
    }
    var results = jsonObject.d.results;
    for (var i = 0; i < results.length; i++)
    {
        var selectOption = document.createElement("option");
        selectOption.value = results[i].LoginName;
        selectOption.innerText = results[i].LoginName;
        RetriveUsers.appendChild(selectOption);
    }
}
function getUsersFromGroupError(data, errorCode, errorMessage)
{
    alert("Could not get users from group: " + 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];
        }
    }

Refer Here: One,