The term function statement has been widely and wrongly used to
describe a FunctionDeclaration. This is misleading because in ECMAScript,
a FunctionDeclaration is not a Statement; there are places in a program
where a Statement is permitted but a FunctionDeclaration is not. To add
to this confusion, some implementations, notably Mozillas', provide a
syntax extension called function statement. This is allowed under
section 16 of ECMA-262, Editions 3 and 5.
Example of nonstandard function statement:
// Nonstandard syntax, found in GMail source code. DO NOT USE.
try {
// FunctionDeclaration not allowed in Block.
function Fze(b,a){return b.unselectable=a}
/*...*/
} catch(e) { _DumpException(e) } Code that uses function statement has three known interpretations. Some
implementations process Fze as a Statement, in order. Others, including
JScript, evaluate Fze upon entering the execution context that it
appears in. Yet others, notably DMDScript and default configuration of BESEN,
throw a SyntaxError.
For consistent behavior across implementations, do not use function
statement; use either FunctionExpression or FunctionDeclaration instead.
Example of FunctionExpression (valid):
var Fze;
try {
Fze = function(b,a){return b.unselectable=a};
/*...*/
} catch(e) { _DumpException(e) } Example of FunctionDeclaration (valid):
// Program code
function aa(b,a){return b.unselectable=a}