In JavaScript, when using the var keyword to declare a variable, the JS engine assigns a default value of "undefined" at creation stage.
console.log(message); // undefined
var message = "My message";
However, with the let keyword:
console.log(message); // message is not defined
let message = "My message";
Why does this result in an unexpected outcome? Could it be due to changes in ES6?
The reason behind this behavior lies in the introduction of Temporal dead zone when using the let keyword
When you declare a variable with
let, it is hoisted to the top of its block scope. However, unlike variables declared withvar, which are initialized withundefined,letvariables remain uninitialized until their value is explicitly set. Trying to access aletvariable before it is initialized will result in aReferenceError. This period where the variable exists but has not been initialized is known as the "temporal dead zone".
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