The main difference between let and var is scope. Variables declared with var have function scope, while variables declared with let have block scope.
A closure is a function that remembers its outer variables and can access them even after the outer function has returned.
Null is a value that represents the absence of a value, while undefined means that a variable has been declared but has not been assigned a value.
The double equal sign (==) performs type coercion, meaning it will try to convert the values to the same type before comparing them. The triple equal sign (===) does not perform type coercion and only returns true if the values are the same type and value.
The main difference between let and const is that variables declared with const are read-only and cannot be reassigned, while variables declared with let can be reassigned.
A function declaration is declared as a statement, while a function expression is declared as part of a larger expression syntax. Function declarations are hoisted, while function expressions are not.
A callback function is a function that is passed as an argument to another function and is executed after a certain event or operation has completed. Callback functions are used to handle asynchronous operations.