The error "Uncaught TypeError" occurs when trying to access undefined properties of an object, specifically when trying to read the "sync" property.

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This error can occur in a variety of contexts, such as when trying to access a property of an uninitialized variable or when attempting to call a method on an object that does not have that method defined. It can also occur when trying to use a variable as an object that is not actually an object, like trying to access an undefined property of a primitive value.

To avoid this error, it's important to make sure all properties and methods being accessed are correctly defined and initialized before attempting to use them. This can be done by checking for null or undefined values before trying to access properties or calling methods on an object. Additionally, using debugging tools like console.log() can help identify the root cause of the error and facilitate troubleshooting.