The invocation operator is a pair of parentheses that follow any expression that produces a function value. The parentheses can contain zero or more expressions, separated by commas. Each expression produces one argument value. Each of the argument values will be assigned to the function's parameter names. There is no runtime error when the number of arguments and the number of parameters do not match. If there are too many argument values, the extra argument values will be ignored. If there are too few argument values, the undefined value will be substituted for the missing values. There is no type checking on the argument values: any type of value can be passed to any parameter.
JavaScript does not have block scope even though its block syntax suggests that it does. This confusion can be a source of errors. JavaScript does have function scope. That means that the parameters and variables defined in a function are not visible outside of the function, and that a variable defined anywhere within a function is visible everywhere within the function.