function Keyword

 The expression is not allowed at the start of a statement.

function (param0) {
  statements
}
function (param0, param1) {
  statements
}
function (param0, param1, /* … ,*/ paramN) {
  statements
}

function name(param0) {
  statements
}
function name(param0, param1) {
  statements
}
function name(param0, param1, /* … ,*/ paramN) {
  statements
}

As of ES2015, you can also use arrow functions.

Parameters

name (Optional)

The function name. Can be omitted, in which case the function is anonymous. The name is only local to the function body.

paramN (Optional)

The name of an argument to be passed to the function.

statements (Optional)

The statements which comprise the body of the function.