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 have not looked into them thoroughly.
Can anyone tell me, can I use lambda syntax in JavaScript?
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.
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
()=>{} etc in Javascript... I did not realise it was just a Typescript extension I had accidentally tripped over. Many thanks. :)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");
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
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
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] } ));