Using semi-colons to close functions in JavaScript. Necessary?

Question

When executing a function in JavaScript, I've always ended my code block with a semi-colon by default, because that's what I've been taught to do. Coming from Java it felt a bit unorthodox at first, but syntax is syntax.

function semiColon(args) {
   // code block here
};

or

function sloppyFunction(args) {
   // code block here
}

Lately I've been seeing more and more code where the developer left the semi-colon out after functions, but the intended code still executed normally. So are they actually required? If not, why is it common practice to include them? Do they serve another purpose?

Answer 1

Function declarations do not need a semi-colon, though if you put a semi-colon there, it won't be harmful, it is just a redundant empty statement.

function semiColon(args) {
   // code block here
};;;; // 4 empty statements

Most statements require a semi-colon, but if you leave the semi-colon out it will be inserted automatically in most cases by Automatic Semi-Colon Insertion, with caveats. In general it is easier to just always add a semi-colon after your statements, so that you, and other developers working with your code, don't have to worry about those caveats.

This code is correct:

function semiColon(args) {
   // code block here
} // No need for semi-colon

var semiColon = function (args) {
   // code block here
}; // Semi-colon required here

Whereas this code is wrong, but will still usually work:

function semiColon(args) {
   // code block here
}; // Redundant unnecessary Empty Statement 

var semiColon = function (args) {
   // code block here
} // Semi-colon required here,
// but ASI will sometimes insert it for you, depending on
// the subsequent token

Answer 2

NO - using semicolons to end function declarations are NOT necessary in JavaScript. While they will not throw an error, they are the equivalent of using more than one semicolon to end a line of code - harmless, but unnecessary. Being superfluous, they are considered poor stylistic and programming practice.

The one exception is a function expression, e.g.

var my_function = function(a, b){ };

where you DO need the semicolon to terminate the line.

Answer 3

You shall not add a semicolon after a function declaration.

Because, after checking the Javascript grammar:

• StatementList:

  • StatementListItem
  • StatementList

• StatementListItem:

  • Statement
  • Declaration

• Declaration:

  • HoistableDeclaration
  • ClassDeclaration
  • LexicalDeclaration

• HoistableDeclaration:

  • FunctionDeclaration
  • GeneratorDeclaration

Here's the grammar production for a function:

FunctionDeclaration → HoistableDeclaration → Declaration → StatementListItem → StatementList

which proves that my former response is wrong (no need to look at the former edits, as it's wrong! ;) ).

A function xx() {} construct alone is a special case, neither — strictly speaking — a statement or an expression, and thus is NOT to be ended with a semicolon.

You only need to add a semicolon (or leave the ASI take care of it) if you're using the expression function() construct, which exists when it is part of a statement. To make it a statement you need to either have it part of a statement:

var foo = function() {};

or embedded within another expression:

(function() {})();
!function x() { ... }();

And in either cases, you need to add the semicolon at the end of the full statement, obviously.

Generally speaking, I like the python mantra "explicit is better than implicit" so when you hesitate to add a semicolon that the ASI would add otherwise, just add it.

sorry for being wrong in the first version of my answer, I'll debug some PHP code as a penitence. ☺

HTH