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by dance2die
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How to Implement LINQ methods in JavaScript - Part 8

Broken Post? → Let me know

Photo by Pau Casals on Unsplash LINQ methods (All, Contains, SequenceEqual) in this article  are somehow related in a way that they are predicates (returns true or false).

Here are the methods covered so far.

  1. Part 1 〰️ Select, Aggregate, Where, OrderBy (Ascending, Descending)
  2. Part 2 〰️ Any, Distinct, Concat, SelectMany
  3. Part 3 〰️ Reverse, Zip, Min/Max
  4. Part 4 〰️ Union, Intersect, Except
  5. Part 5 〰️ Sum, Average, Count
  6. Part 6 〰️ First, Last, DefaultIfEmpty, Skip, Take
  7. Part 7 〰️ Empty, Repeat, Range
  8. Part 8 〰️ All, Contains, SequenceEqual

🔴 Overview

In this article, I will cover following methods.

[table id=9 /]

The sample collections used in this part are shown as below.

C#

private static List<Order> Orders = new List<Order>{
new Order(id: 1, quantity: 40, orderDate: new DateTime(2018, 1,1,1,1,1,1)),
new Order(id: 2, quantity: 20, orderDate: new DateTime(2018, 2,2,2,2,2,2)),
new Order(id: 3, quantity: 30, orderDate: new DateTime(2018, 3,3,3,3,3,3)),
new Order(id: 4, quantity: 10, orderDate: new DateTime(2018, 4,4,4,4,4,4)),
new Order(id: 5, quantity: 20, orderDate: new DateTime(2018, 5,5,5,5,5,5)),
};
private static List<Order> DomesticOrders = new List<Order>{
new Order(id: 1, quantity: 40, orderDate: new DateTime(2018, 1,1,1,1,1,1)),
new Order(id: 11, quantity: 20, orderDate: new DateTime(2018, 11,2,2,2,2,2)),
new Order(id: 111, quantity: 450, orderDate: new DateTime(2018, 11,1,2,2,2,2)),
new Order(id: 1111, quantity: 230, orderDate: new DateTime(2018, 11,11,2,2,2,2)),
};
view raw Blog Part 8.cs hosted with ❤ by GitHub

JavaScript

const orders = [
{ id: 1, quantity: 40, orderDate: new Date(2018, 1, 1, 1, 1, 1) },
{ id: 2, quantity: 20, orderDate: new Date(2018, 2, 2, 2, 2, 2) },
{ id: 3, quantity: 30, orderDate: new Date(2018, 3, 3, 3, 3, 3) },
{ id: 4, quantity: 10, orderDate: new Date(2018, 4, 4, 4, 4, 4) },
{ id: 5, quantity: 20, orderDate: new Date(2018, 5, 5, 5, 5, 5) }
];
const domesticOrders = [
{ id: 1, quantity: 40, orderDate: new Date(2018, 1, 1, 1, 1, 1) },
{ id: 11, quantity: 20, orderDate: new Date(2018, 11, 2, 2, 2, 2) },
{ id: 111, quantity: 450, orderDate: new Date(2018, 11, 1, 2, 2, 2) },
{ id: 1111, quantity: 230, orderDate: new Date(2018, 11, 11, 2, 2, 2) }
];
view raw Blog Part 8.js hosted with ❤ by GitHub

🔴 Examples

🔸 All

JavaScript has a method called Array#every, which works the same way as All does.

private static void AllDemo(List<Order> orders)
{
var areAllOrdersPlacedOn2018 = orders.All(order => order.OrderDate.Year == 2018);
WriteLine($"Are All Orders Placed On 2018?: {areAllOrdersPlacedOn2018}");
}
view raw AllDemo.cs hosted with ❤ by GitHub

function allDemo(orders) {
const areAllOrdersPlacedOn2018 = orders.every(
order => order.orderDate.getFullYear() === 2018
);
WriteLine(`Are All Orders Placed On 2018?: ${areAllOrdersPlacedOn2018}`);
}
view raw allDemo.js hosted with ❤ by GitHub

Results

// C#
==================== All DEMO - Check If All Orders Match a Condition ====================
Are All Orders Placed On 2018?: True
// JS
==================== All DEMO - Check If All Orders Match a Condition ====================
Are All Orders Placed On 2018?: true
view raw All Demo Results hosted with ❤ by GitHub

every is more flexible as the callback is also passed an index.

array#every syntax

🔸 Contains

There are so many ways implement contains but i used some as it short circuits (returns as soon as a condition is met).

private static void ContainsDemo(List<Order> shippedOrders, List<Order> domesticOrders)
{
var firstDomesticOrder = domesticOrders.First();
var containsDomesticOrder = shippedOrders.Contains(firstDomesticOrder, new OrderEqualityCompaprer());
WriteLine($"Is the first domestic order shipped? {containsDomesticOrder}");
}
view raw ContainsDemo.cs hosted with ❤ by GitHub

function containsDemo(shippedOrders, domesticOrders) {
const firstDomesticOrder = domesticOrders[0];
const equalityComparer = order => order.id === firstDomesticOrder.id;
const containsDomesticOrder = shippedOrders.some(equalityComparer);
WriteLine(`Is the first domestic order shipped? ${containsDomesticOrder}`);
}
view raw containsDemo.js hosted with ❤ by GitHub

Results

// C#
==================== Contains DEMO - Do Shipped Orders Contain a Domestic Order? ====================
Is the first domestic order shipped? True
// JS
==================== Contains DEMO - Do Shipped Orders Contain a Domestic Order? ====================
Is the first domestic order shipped? true
view raw Conains Demo Results hosted with ❤ by GitHub

OrderEqualityComparer object instance simply checks if two objects are the same by an ID. JavaScript version simply passes a callback which does the same.

🔸 SequenceEqual

You can use every here to check if two sequences are the same as every passes an index of current element to the callback.

private static void SequenceEqualDemo(List<Order> shippedOrders, List<Order> domesticOrders)
{
var sameOrderAreSame = shippedOrders.SequenceEqual(shippedOrders);
WriteLine($"Same Orders share the same sequence {sameOrderAreSame}");
var areAllDomesticOrdersShipped = shippedOrders.SequenceEqual(domesticOrders);
WriteLine($"Are All Domestic Order Shipped? {areAllDomesticOrdersShipped}");
}
view raw SequenceEqualDemo.cs hosted with ❤ by GitHub

function sequenceEqualDemo(shippedOrders, domesticOrders) {
const sameOrderAreSame = shippedOrders.every(
(order, i) => order.id === shippedOrders[i].id
);
WriteLine(`Same Orders share the same sequence ${sameOrderAreSame}`);
const areAllDomesticOrdersShipped = shippedOrders.every(
(order, i) => order.id === domesticOrders[i].id
);
WriteLine(`Are All Domestic Order Shipped? ${areAllDomesticOrdersShipped}`);
}
view raw sequenceEqualDemo.js hosted with ❤ by GitHub

Results

// C#
==================== SequenceEqual DEMO - Check If Two Sequences Are The Same ====================
Same Orders share the same sequence True
Are All Domestic Order Shipped? False
// JS
==================== SequenceEqual DEMO - Check If Two Sequences Are The Same ====================
Same Orders share the same sequence true
Are All Domestic Order Shipped? false
view raw SequenceEqual Demo Results hosted with ❤ by GitHub

🔴 Closing Remark

I hope this article can serve as a cheat sheet (that's how I started this series).

Please let me know should you find any errors or improvements I can make to the codes. The full source code and instructions on how to run them are on GitHub.