Java Script Syntax - Functions

Functions

A function is a block with a (possibly empty) parameter list that is normally given a name. A function may use local variables. If you exit the function without a return statement, the value undefined is returned.

function gcd(segmentA, segmentB) { var diff = segmentA - segmentB; if (diff == 0) return segmentA; return diff > 0 ? gcd(segmentB, diff) : gcd(segmentA, -diff); } alert(gcd(60, 40)); // 20 var mygcd=gcd; // mygcd is a reference to the same function as gcd. Note no argument s. alert(mygcd(60, 40)); // 20

Functions are first class objects and may be assigned to other variables.

The number of arguments given when calling a function may not necessarily correspond to the number of arguments in the function definition; a named argument in the definition that does not have a matching argument in the call will have the value undefined (which can be implicitly cast to false). Within the function, the arguments may also be accessed through the arguments object; this provides access to all arguments using indices (e.g. arguments, arguments, ... arguments), including those beyond the number of named arguments. (While the arguments list has a .length property, it is not an instance of Array; it does not have methods such as .slice, .sort, etc.)

function add7(x, y) { if (!y) { y = 7; } alert(x + y + arguments.length); }; add7(3); // 11 add7(3, 4); // 9

All parameters are passed by value (for objects, it is the reference to the object that is passed).

var obj1 = {a : 1}; var obj2 = {b : 2}; function foo(p) { p = obj2; // Ignores actual parameter p.b = arguments; } foo(obj1, 3); // Does not affect obj1 at all. 3 is additional parameter alert(obj1.a + " " + obj2.b); // writes 1 3

Functions can be declared inside other functions, and access the outer function's local variables. Furthermore they implement full closures by remembering the outer function's local variables even after the outer function has exited.

var v = "Top"; var bar, baz; function foo { var v = "fud"; bar = function { alert(v) }; baz = function(x) { v = x; }; } foo; baz("Fugly"); bar; // Fugly (not fud) even though foo has exited. alert(v); // Top

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Famous quotes containing the word functions:

    Those things which now most engage the attention of men, as politics and the daily routine, are, it is true, vital functions of human society, but should be unconsciously performed, like the corresponding functions of the physical body.
    Henry David Thoreau (1817–1862)

    The English masses are lovable: they are kind, decent, tolerant, practical and not stupid. The tragedy is that there are too many of them, and that they are aimless, having outgrown the servile functions for which they were encouraged to multiply. One day these huge crowds will have to seize power because there will be nothing else for them to do, and yet they neither demand power nor are ready to make use of it; they will learn only to be bored in a new way.
    Cyril Connolly (1903–1974)

    Empirical science is apt to cloud the sight, and, by the very knowledge of functions and processes, to bereave the student of the manly contemplation of the whole.
    Ralph Waldo Emerson (1803–1882)