In this simple code, since the variable b is a let variable and i am trying to log() its value, I was expecting a reference error that said: cannot access ‘a’ before initialization,
but instead i am getting the error:
Uncaught ReferenceError: a is not defined
console.log(a);
let a=10;
var b=19;
a screenshot of the code and the error–>
i ran the same code in online js editors and they give the expected error, i am confused now :
the same code on an online editor with different error
2
Answers
The reason you’re getting a Uncaught ReferenceError: a is not defined error instead of the expected cannot access ‘a’ before initialization is due to a difference in how let and var declarations are hoisted in JavaScript.
When you use let to declare a variable, the variable is hoisted to the top of its block scope, but it is not initialized until the actual declaration statement is encountered in the code. That’s why you get a ReferenceError when you try to access the variable before its declaration.
On the other hand, when you use var to declare a variable, it is hoisted to the top of its function or global scope, and it’s initialized with undefined at that point. Therefore, accessing a var variable before its declaration results in undefined rather than a ReferenceError.
According to error docs it
happens within any block statementSince you don’t have block statement, JS fires another error.
I suppose that in online editor, the code is executed by another code, so there could be block statement outside the "file".