How to check if a variable exists in JavaScript (defined/initialized)?

Hello everyone! I just started learning JavaScript and encountered a problem. I have code where I'm trying to use a variable, but it may not be defined. I want to check if a variable exists (i.e., has been declared and initialized) before using it. For example, I have this code: ```javascript var myVar; console.log(myVar); // undefined console.log(typeof myVar); // "undefined" if (myVar) { console.log("Variable exists!"); } ``` But here I understand that `myVar` is declared but not initialized, so `typeof` shows `"undefined"`. What if the variable is not declared at all? ```javascript if (unknownVar) { console.log("This variable does not exist!"); } ``` This code throws an error `ReferenceError: unknownVar is no