The problem with let, const or var is you can define multiple variable
after them, and it's ambiguous which one must be returned from the
expression. But like comma expression which would return the last part as a
result, the let and const also should return the last assignment as the
result so it can be used inside parentheses
(let a = 1, b = 2) === 2
A common type of code in JS is searching for element and do something with
them:
let e1 = document.getElementById('id1');
if (e1) this.AppendChild(e);
let e2 = document.getElementById('id2');
if (e2) this.AppendChild(e);
This pattern can really help encapsulation and readability;
if (let e = document.getElementById('id1')) this.AppendChild(e);
if (let e = document.getElementById('id2')) this.AppendChild(e);
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