Intro

Linq in c# is a great abstraction, it massively reduces the amount of code to do fairly basic operations, using TypeScript doesn’t mean you lose this functionality, its just a little different to achieve many of the operations. In this article I’ll run through the basic Linq-To-Object operations, and how you can achieve similar results in TypeScript.

For these examples, I’ll keep it simple with a list of Person objects that look like this:

      public class Person{
       public string Name {get;set;}
       public string Title {get;set;}
   }
     

   class Person
{
    constructor(public Name: string, public Title: string)
    { }
}
     

(How good is that typescript constructor/field syntax!).

With the data:

• Chandler - Mr
• Monica - Mrs
• Rachel - Miss
• Joey - Mr
• Ross - Dr

Select

To select the names of each person with their title:

CSharp

people.Select(x => new { FullTitle = $"{x.Title} {x.Name}"});

Typescript

In TypeScript, the equivalent to select is the map function:

people.map(x => ({ FullTitle: x.Title + ' ' + x.Name }));

Where

To filter the list to only the people with the title “Mr”:

CSharp

people.Where(x => x.Title == "Mr");

Typescript

people.filter(x => x.Title == "Mr");

OrderBy

To order the list by Name:

CSharp

people.OrderBy(x => x.Name);

Typescript

In TypeScript, the equivalent to order by is the sort function, but you do have to give it a sort function that returns 1 or 0:

people.sort((x,y) => x.Name > y.Name ? 1 : -1);

GroupBy

To group the list into the various titles:

CSharp

people.GroupBy(x => x.Title);

Typescript

There isn’t a simple equivalent to this, the closest thing is probably the reduce function:

var grouped = people.reduce((g : any, person : Person) => {
    g[person.Title] = g[person.Title] || []; //Check the value exists, if not assign a new array
    g[person.Title].push(person); //Push the new value to the array
    return g; //Very important! you need to return the value of g or it will become undefined on the next pass
}, {});

FirstOrDefault

To select the first person with the title Mr, or null if none exist:

CSharp

people.FirstOrDefault(x => x.Title == "Mr");

Typescript

people.find(x => x.Title == "Mr");

Aggregate

Lets concatenate all the names together:

CSharp

people.Select(x => x.Name).Aggregate((x,y) => x = x + "" + y).Dump();

Typescript

This time, reduce is almost like for like with the c# equivalent

var concat = people.map(x => x.Name).reduce((g : any, name: string) => {
    g += name;
    return g;
}, "");