The Temporal Dead Zone is a concept introduced in ECMAScript 2015 (ES6) as part of the
let and const variable declarations. It is a specific
region within a scope where variables exist but cannot be accessed until they are assigned a
value. This zone starts at the beginning of the scope and continues until the point of
When a variable is accessed within the TDZ, a ReferenceError is thrown, indicating that the variable is not yet initialized. This behavior is different from traditional variable hoisting, which we will discuss in the next section.
To understand the differences between the Temporal Dead Zone and hoisting, let's summarize their contrasting characteristics:
Let's consider a few examples to illustrate the behavior of TDZ and hoisting:
console.log(myVariable); // Throws a ReferenceError
let myVariable = 42;
In this example, we attempt to access myVariable before it is declared, resulting in a ReferenceError due to the TDZ.
console.log(myVariable); // Outputs 'undefined'
var myVariable = 42;
In this case, myVariable is hoisted to the top of the scope, but its value
is not assigned until later in the code. As a result, the initial value is
To prevent pitfalls related to TDZ and hoisting, consider the following best practices: