Angular.js linq.js Where filter not working properly

I am using linq.js in AngularJs, I am using in many places and its working fine now I used in different place and it doesn't work for me. Not working means I am not achieving the desired result it always showing {}. please take a look below code if I am doing something wrong.

var app = angular.module('testApp', ['angular.filter', 'angular-linq', 'ngSelect2']);
    app.controller('testController', function ($scope, $http, $timeout, $q, $linq){
    $scope.Vendors = 
    [
      {VendorId:"VND001", VendorName:"Pharma Plus Pharmacy", Address:"Bahawalpur"},
      {VendorId:"VND001", VendorName:"Pakistan Pharma", Address:"Bahawalpur"}
    ];
    $scope.InvoiceItems = 
    [
     {
        VendorId:"VND001", 
        ItemName:"Gold Set Jewellery", 
        ItemDesc:"Some Description", 
        Cost:280.50, 
        Quantity:50 
     },
     {
        VendorId:"VND001", 
        ItemName:"First Class HandWatch", 
        ItemDesc:"Some Description", 
        Cost:100.50, 
        Quantity:50 
     },
     {
        VendorId:"VND002", 
        ItemName:"Gold Set Jewellery", 
        ItemDesc:"Some Description", 
        Cost:280.50, 
        Quantity:50 
     },
     {
        VendorId:"VND002", 
        ItemName:"First Class HandWatch", 
        ItemDesc:"Some Description", 
        Cost:100.50, 
        Quantity:50 
     },
    ];
    $scope.totalAmount = function(vendorId){
       return $linq.Enumerable().From($scope.InvoiceItems).Where("x => x.VendorId =="+vendorId).Select(function(x){
          return (+x.Cost)*x.Quantity;
       }).Sum();
    }
  }
}

Please take a look below html

<div class="row" ng-app="testApp">
  <div class="col-xs-12" ng-controller="testController" ng-init="initializeDefault()">
    <div ng-repeat="v in Vendors">
        <div>{{ v.VendorId }}</div>
        <div>{{ v.VendorName }}</div>
        <div>{{ v.Address }}</div>
        <div>{{ totalAmount(v.VendorId) }}</div>
    </div>
  </div>
</div>

Prompt response will be appreciated.

The first problem I see is that your predicate in the where clause is malformed.

The x.VendorId is a string and you're trying to compare it to the passed in vendorId. But the lambda you generate is effectively:

x => x.VendorId ==VND001

which would yield no results.

Instead you need to generate:

x => x.VendorId == 'VND001'

Your query ought to be (using the more compact lambda syntax):

$linq.Enumerable().From($scope.InvoiceItems)
    .Where("$.VendorId == '" + vendorId + "'")
    .Select("+$.Cost * $.Quantity")
    .Sum();

However, it would be better if you combined those queries up front and include the total sum as part of the query, rather than a separate one. You'll have to join the two arrays.

$scope._vendors = ...;
$scope._invoiceItems = ...;
$scope.VendorQuery = function() {
    return $linq.Enumerable().From($scope._vendors)
        .GroupJoin($scope._invoiceItems, "$.VendorId", "$.VendorId",
            "{ Id: $.VendorId, Name: $.VendorName, Address: $.Address, "
            + "Total: $$.Sum('+$.Cost * $.Quantity') }")
        .ToArray();
}

Then bind to your view:

<div ng-repeat="v in VendorQuery()">
    <div>{{ v.Id }}</div>
    <div>{{ v.Name }}</div>
    <div>{{ v.Address }}</div>
    <div>{{ v.Total }}</div>
</div>