ReferenceError: cannot access before initialization

2 min readJul 24, 2024

In this article, we will delve into the intricacies of a common JavaScript error known as “ReferenceError: Cannot Access Before Initialization.”

We will explore the reasons behind this error and provide comprehensive solutions to help you resolve it effectively.

What is ReferenceError cannot access before initialization?

The “ReferenceError: Cannot access before initialization” error happens when a variable declared with let or const is accessed before it has been initialized within the scope.

Here is how this error occurs:

// 📌 ReferenceError: Cannot access 'arr' before initialization
arr = [3, 2, 1];
let arr = [1, 2, 3];
if (5 === 5) {
  // 📌ReferenceError:
  console.log(num);
  const num = 100;
}
function example() {
  // 📌ReferenceError:
  console.log(str);
  let str = 'bobbyhadz.com';
}
// 📌ReferenceError:
const result = sum(5, 10);
const sum = (a, b) => {
  return a + b;
};

Potential causes of ReferenceError

A common reason for this error is connected to the variable scope.

When you use the let or const keywords to declare a variable inside a block or function, it becomes scoped to that block or function.

Thus, if you attempt to access the variable before declaring it within that scope, the error occurs.

Furthermore, in asynchronous JavaScript, like promises or async/await, the execution order can differ.

If you try to access a variable or function that depends on asynchronous operations before it’s initialized or resolved, an error may occur.

Meanwhile, in JavaScript, “hoisting” is when variable and function declarations are moved to the top during compilation.

Wherein Declarations are hoisted, but not initialization.

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In addition, trying to access a variable before declaring it, even with hoisting, results in a “ReferenceError: Cannot Access Before Initialization” error.

Solutions — ReferenceError cannot access before initialization

Initialize the variable before accessing it

The first way to resolve the error is to make sure to initialize the variables before utilizing them.