Uncaught TypeError: Cannot read properties of undefined (reading 'open')

This error occurs when you try to access a property or method of an undefined variable or object. In this case, it seems like you are trying to access the 'open' property of an undefined variable or object.

To fix this error, you need to check if the variable or object is defined before trying to access its properties or methods. You can use an if statement to check if the variable or object exists before trying to access its properties or methods.

For example:

let xhr = new XMLHttpRequest();

if (xhr) {
  xhr.open('GET', 'https://example.com/api');
  // rest of the code
}

In this example, we check if the xhr variable exists before calling the 'open' method. If xhr is undefined, the code inside the if statement will not be executed, preventing the 'Cannot read properties of undefined' error.