[FIXED] Why Field declarations have no keywords in Javascript ES6?

Issue

class MyDemo{
  let x =5;
}

We can get an error. But when we remove the let keyword, it would be correct. I want to know why this happend.

Solution

let is used to create a new standalone identifier - a variable name. Directly inside a class, assignment is using class instance field syntax to assign to a property of the instance.

That is, this

class MyDemo {
  x = 5;
}

means you can then do

const demo = new MyDemo();
console.log(demo.x); // logs 5

x is not a new identifier with a particular block scope - rather, it's a property of the object, so it wouldn't have made sense if the syntax required (or even permitted) them to be preceded by let (or const).

A property of an object, with a particular configuration (getter, setter, configurable, writable) is a pretty different concept from a standalone identifier (declared with const, let, or var). Mixing the two, like your code does, would just have been too misleading.

Answered By - CertainPerformance

Answer Checked By - Marilyn (PHPFixing Volunteer)