Is there a C#-like lambda syntax in JavaScript?

Question

Is there a framework or post processor for JavaScript that supports lambda syntax like in C#?

Function definitions in CoffeeScript seem to look like lambdas but I ha

Answer 1

You could use typescript (www.typescriptlang.org/):

function (d, i) {
    return "translate(" + d.x + "," + d.y + ")";
}

would become

(d, i) =>  "translate(" + d.x + "," + d.y + ")"  

and much more cool stuff, like typing: ... that's if you are into that

Answer 2

I started creating an extender for jQuery which does exactly the thing you are asking. JS-Lambda

For example in C#:

  coll.TakeWhile(x => x.index < 3);

Looks like:

 $(coll).TakeWhile("x => x.index < 3");

Answer 3

Javascript has very nice anonymous functions that allows you to create lambdas anyWhere you need as a function but the implementation comes with some much words and scope creation repeating:

function(name){
     return "Hello, " + name;
}

Thanks to EcmaScript 2015 lambda expresion is now available for javaScript with simpler syntax as Arrow Function

(name) => "Hello, " + name

Answer 4

Exact Matthew Mcveigh!!

I want to contribute too, see this example

"use strict";
/* Lambda Helper to print  */
function PrintLineForElement(element, index, array){
  document.write("a[" + index + "] = " + JSON.stringify(element)+"<br>");
}
/* function to print array */
function Print(a){
   a.forEach(PrintLineForElement)
   document.write("<br>");
}
/* user model */
class User{
		constructor(_id,_name,_age,_job){
			 this.id = _id;
       this.name = _name;
			 this.age = _age;
       this.job = _job;
		}
} 
/* Provaider users */
class UserService{ 

		constructor(){ } 
    
		GetUsers(){
        //fake ajax response
				let data = [];	
        data.push(new User(1,"Juan",20,"AM"));
        data.push(new User(2,"Antonio",20,"AM"));
        data.push(new User(3,"Miguel Angel",30,"Developer"));
        data.push(new User(4,"Bea",26,"AM"));
        data.push(new User(5,"David",24,"Developer")); 
        data.push(new User(6,"Angel",24,"Developer")); 
        data.push(new User(7,"David",34,"TeamLead"));
        data.push(new User(8,"Robert",35,"TeamLead"));
        data.push(new User(9,"Carlos",35,"TeamLead"));   
				
        return data;
		}
}

const userService = new UserService();
const users =  userService.GetUsers();

//get user order by name
document.write("All users </br>");
Print(users);

//get user order by name
document.write("Order users by name ASC : users.sort((a,b)=>{return a.name > b.name })</br>");
Print(users.sort((a,b)=>{return a.name > b.name; }));
document.write("Order users by name DESC : users.sort((a,b)=>{return a.name < b.name })</br>");
Print(users.sort((a,b)=>{return a.name < b.name; }));

//get user filter by age 
document.write("Only users oldest or equal than 25 : users.filter( (w) => {return w.age >= 25;} )</br>");
Print(users.filter( (w) => {return w.age >= 25;} )); 
document.write("Only users smallest or equal than 25 : users.filter( (w) => {return w.age <= 25;} )</br>");
Print(users.filter( (w) => {return w.age <= 25;} )); 

//GroupBY 
/**
* custom group by with Array.prototype.keys
**/

Array.prototype.groupBy = function(f)
{
  let groups = [];
  this.forEach( function( o )
  {
    let group =  f(o) ;
    groups[group] = groups[group] || [];
    groups[group].push( o );  
  });

  return Object.keys(groups).map( function( group )
  {
    return groups[group]; 
  })
}

document.write("Group user by age </br>");
Print(users.groupBy( (w) => {return w.age } )); 

document.write("Group user by job </br>");
Print(users.groupBy( (w) => {return w.job } )); 

document.write("Group user by job</br>");
Print(users.groupBy( (g) => {return [g.job] } ));

document.write("Group user by job and age then order by name </br>");
Print(users.sort((a,b)=>{return a.job > b.job}).groupBy( (g) => {return [g.job+g.age] } ));

document.write("Group user by job and age then order by name and filter where age < 25 and job equal AM </br>");
Print(users.sort((a,b)=>{return a.job > b.job}).filter((w)=>{ return w.age<25 || w.job == "AM" }).groupBy( (g) => {return [g.job+g.age] } ));

https://jsfiddle.net/angelfragap/0b5epjw3/29/

Answer 5

FIDDLE: https://jsfiddle.net/vktawbzg/

NPM: https://www.npmjs.com/package/linqscript

GITHUB: https://github.com/sevensc/linqscript

using Typescript i created a class List<T> which extends Array<T>

usage:

var list = new List<ListView>();
...
var selected = list.Items.Where(x => x.Selected);

implementation:

 export class List<T> extends Array<T> {

    public Where(callback: (value: T) => boolean, thisArg?: any): List<T> {
            try {
                const list = new List<T>();

                if (this.length <= 0)
                    return list;

                if (typeof callback !== "function")
                    throw new TypeError(callback + ' is not a function');

                for (let i = 0; i < this.length; i++) {
                    const c = this[i];
                    if (c === null)
                        continue;

                    if (callback.call(thisArg, c))
                        list.Add(c);
                }

                return list;
            }
            catch (ex) {
                return new List<T>();
            }
        }
...
}

EDIT: I created a github repo: https://github.com/sevensc/linqscript

Answer 6

Lambda functions with similar syntax are included in ECMAscript 6, they're known as "arrow functions". An example:

["duck", "cat", "goat"].filter(el => el.length > 3); returns ["duck", "goat"]

There's currently support in recent versions of Firefox and Chrome.

To use this syntax in JavaScript that's targeting older browsers there are tools that can compile ES 6 to a more widely supported version - for example the tools Babel or Traceur.