Javascript – use a semicolon after every function in javascript

javascriptsyntax

I've seen different developers include semicolons after functions in javascript and some haven't. Which is best practice?

function weLikeSemiColons(arg) {
   // bunch of code
};

function unnecessary(arg) {
  // bunch of code
}

Best Answer

Semicolons after function declarations are not necessary.

The grammar of a FunctionDeclaration is described in the specification as this:

function Identifier ( FormalParameterListopt ) { FunctionBody }

There's no semicolon grammatically required, but might wonder why?

Semicolons serve to separate statements from each other, and a FunctionDeclaration is not a statement.

FunctionDeclarations are evaluated before the code enters into execution, hoisting is a common word used to explain this behaviour.

The terms "function declaration" and "function statement" are often wrongly used interchangeably, because there is no function statement described in the ECMAScript Specification, however there are some implementations that include a function statement in their grammar, -notably Mozilla- but again this is non-standard.

However semicolons are always recommended where you use FunctionExpressions, for example:

var myFn = function () {
  //...
};

(function () {
  //...
})();

If you omit the semicolon after the first function in the above example, you will get completely undesired results:

var myFn = function () {
  alert("Surprise!");
} // <-- No semicolon!

(function () {
  //...
})();

The first function will be executed immediately, because the parentheses surrounding the second one, will be interpreted as the Arguments of a function call.

Recommended lectures:

Named function expressions demystified (great article)
Explain JavaScript’s encapsulated anonymous function syntax (more on FunctionDeclaration vs FunctionExpression)

Related Solutions

Javascript – Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”

I use javascript:void(0).

Three reasons. Encouraging the use of # amongst a team of developers inevitably leads to some using the return value of the function called like this:

function doSomething() {
    //Some code
    return false;
}

But then they forget to use return doSomething() in the onclick and just use doSomething().

A second reason for avoiding # is that the final return false; will not execute if the called function throws an error. Hence the developers have to also remember to handle any error appropriately in the called function.

A third reason is that there are cases where the onclick event property is assigned dynamically. I prefer to be able to call a function or assign it dynamically without having to code the function specifically for one method of attachment or another. Hence my onclick (or on anything) in HTML markup look like this:

onclick="someFunc.call(this)"

onclick="someFunc.apply(this, arguments)"

Using javascript:void(0) avoids all of the above headaches, and I haven't found any examples of a downside.

So if you're a lone developer then you can clearly make your own choice, but if you work as a team you have to either state:

Use href="#", make sure onclick always contains return false; at the end, that any called function does not throw an error and if you attach a function dynamically to the onclick property make sure that as well as not throwing an error it returns false.

Use href="javascript:void(0)"

The second is clearly much easier to communicate.

Javascript – When should I use double or single quotes in JavaScript

The most likely reason for use of single vs. double in different libraries is programmer preference and/or API consistency. Other than being consistent, use whichever best suits the string.

Using the other type of quote as a literal:

alert('Say "Hello"');
alert("Say 'Hello'");

This can get complicated:

alert("It's \"game\" time.");
alert('It\'s "game" time.');

Another option, new in ECMAScript 6, is template literals which use the backtick character:

alert(`Use "double" and 'single' quotes in the same string`);
alert(`Escape the \` back-tick character and the \${ dollar-brace sequence in a string`);

Template literals offer a clean syntax for: variable interpolation, multi-line strings, and more.

Note that JSON is formally specified to use double quotes, which may be worth considering depending on system requirements.

Best Answer

Related Solutions

Javascript – Which “href” value should I use for JavaScript links, “#” or “javascript:void(0)”

Javascript – When should I use double or single quotes in JavaScript

Related Topic