future

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Next Release

ECMAScript 6 is the next draft version of the standard, code-named “Harmony” or “ES.next”. Draft 12 was released November 22, 2012.^[1]

Syntax

There has been a wide range of changes in regards to syntax, below are some examples of syntax additions and changes.

let

Let and const are new ways to declare variables, firstly let is exactly the same as var apart from it bounds the declared variable to the inner-most scope. example:

 //Testing var scope
 function scope()
 {
   for(var i = 0; i != 10; i++)
   {
      //(i) is available here
   }
   //(i) is also available here
 }

 //Testing let scope
 function scope()
 {
   for(let i = 0; i != 10; i++)
   {
      //(i) is available here
   }
   //(i) is *not* available here!
 }

This may not seem like a huge change but it’s actually a much needed feature. An example of ES3/5 would be:

 for(var i = 0; i < 10; i++)
 {
    setTimeout(function(){
      alert(i);
    }, 20);
 }

The above statement will alert the number 10, ten times. this is because the loop iterations finish before the execution of the time-out, so the value of i will be the last possible value in the loop.

Using let allows you to scope the variable to the current iteration scope, meaning that the example below act’s like your creating an anonymous function for every iteration.

 for(let i = 0; i < 10; i++)
 {
    let k = i;
    setTimeout(function(){
      alert(k);
    });
 }

const

const is similar to let and var apart from the variable is marked as read-only.

for…of

for(x of y) loops allow you to iterate over arrays in the same way you iterate over object’s key. an example usage would be:

 let array = [0,2,4,8,16,32,64];
 for(num of array)
 {
 }

Features

TODO: List some of the EMCAScript 6 features such as Syntax, Structures and Library implementations

Concepts

Describe concepts such as Classes, Private Names, Inheritance and Abstraction.

References

1. ↑ ECMAScript 6 Draft 12 “harmony:specification_drafts”. 17-Dec-2004. http://wiki.ecmascript.org/doku.php?id=harmony:specification_drafts#current_working_draft.