Example using purescript-sforce

Main.js

// Generated by purs version 0.12.0
"use strict";
var Control_Bind = require("../Control.Bind/index.js");
var Data_Either = require("../Data.Either/index.js");
var Data_Function = require("../Data.Function/index.js");
var Effect = require("../Effect/index.js");
var Effect_Aff = require("../Effect.Aff/index.js");
var Effect_Class = require("../Effect.Class/index.js");
var Effect_Console = require("../Effect.Console/index.js");
var Prelude = require("../Prelude/index.js");
var Salesforce_Client = require("../Salesforce.Client/index.js");
var Salesforce_Types = require("../Salesforce.Types/index.js");
var queryAccounts = function (conn) {
    return Effect_Class.liftEffect(Effect_Aff.monadEffectAff)(Salesforce_Client.getAccounts(conn));
};
var main = (function () {
    var loginOpts = {
        loginUrl: "https://test.salesforce.com",
        clientId: "-------",
        redirectUri: "http://localhost:8080/",
        proxyUrl: "http://localhost:3123/proxy/"
    };
    var handleLoginSuccess = function (conn) {
        return function __do() {
            Effect_Console.log("connected")();
            return Effect_Aff.launchAff_(Salesforce_Types.runSalesforce(queryAccounts)(conn))();
        };
    };
    var handleLoginError = function (result) {
        if (result instanceof Salesforce_Client.Cancelled) {
            return Effect_Console.log("cancelled");
        };
        if (result instanceof Salesforce_Client["Error"]) {
            return Effect_Console.log(result.value0);
        };
        throw new Error("Failed pattern match at Main line 27, column 31 - line 29, column 27: " + [ result.constructor.name ]);
    };
    return function __do() {
        var v = Salesforce_Client.mkClient()(loginOpts)();
        return Effect_Aff.launchAff_(Control_Bind.bind(Effect_Aff.bindAff)(Salesforce_Client.login()({})(v))(function (v1) {
            return Effect_Class.liftEffect(Effect_Aff.monadEffectAff)(Data_Either.either(handleLoginError)(handleLoginSuccess)(v1));
        }))();
    };
})();
module.exports = {
    main: main,
    queryAccounts: queryAccounts
};

Main.purs

module Main where

import Prelude
import Data.Either (either)
import Effect (Effect)
import Effect.Class
import Effect.Console (log)
import Effect.Aff
import Salesforce.Client
import Salesforce.Types

main :: Effect Unit
main = do
  client <- mkClient loginOpts
  launchAff_ do
    eitherLogin <- login {} client 
    liftEffect $ either handleLoginError handleLoginSuccess eitherLogin

  where 
    loginOpts = 
      {
        loginUrl: "https://test.salesforce.com",
        clientId: "...",
        redirectUri: "http://localhost:8080/",
        proxyUrl: "http://localhost:3123/proxy/"
      }
    handleLoginError result = case result of
      Cancelled -> log "cancelled"
      Error msg -> log msg
    handleLoginSuccess conn = do 
      log "connected"
      launchAff_ $ runSalesforce queryAccounts conn


queryAccounts :: SalesforceM (Array Accounts)
queryAccounts = SalesforceM \conn -> do
    liftEffect $ getAccounts conn