Functions with no return value are sometimes called procedures.

The above code snippet contains nested function in which the function hypotenuse(a,b) has another function inside its scope, function square(x). The interesting thing about nested functions is their variable scoping rules. They can acceess the parameters and variables of the function (or functions) they are nested within.

The function definitions begin with the keyword function followed by an identifier that names the function and a pair of parantheses around a comma-separated list of zero or more identifiers.

The above code snippet returns undefined.

The code above is an invocation expression: it includes a function expression o.m and two argument expressions, x and y.

Even if the string value passed as a parameter to eval does represent a numeric value the use of eval() results in an error being generated.

The function name is optional for functions defined as expressions. A function declaration statement actually declares a variable and assigns a function object to it.

The unshift() and shift() methods behave much like push() and pop(), except that they insert and remove elements from the beginning of an array rather than from the end. unshift() adds an element or elements to the beginning of the array, shifts the existing array elements up to higher indexes to make room, and returns the new length of the array. shift() removes and returns the first element of the array, shifting all subsequent elements down one place to occupy the newly vacant space at the start of the array.

The map() method passes each element of the array on which it is invoked to the functionyou specify, and returns an array containing the values returned by that function.

The return statement causes the function to stop executing and to return the value of its expression (if any) to the caller.

If the return statement does not have an associated expression, it returns the undefined value.

The typeof property is used to identify the array type.