JavaScript Patterns 2.9 Coding Conventions

It’s important to establish and follow coding conventions—they make your code consistent, predictable, and much easier to read and understand. A new developer joining the team can read through the conventions and be productive much sooner, understanding the code written by any other team member.

Indentation

The rule is simple—anything within curly braces. This means the bodies of functions, loops (do, while, for, for-in), ifs, switches, and object properties in the object literal notation.

function outer(a, b) {
    var c = 1,
    d = 2,
    inner;
    if (a > b) {
        inner = function () {
            return {
                r: c - d
            };
        };
    } else {
        inner = function () {
            return {
                r: c + d
            };
        };
    }
    return inner;
} 

Curly Braces

Curly braces should always be used, even in cases when they are optional.

// bad practice
for (var i = 0; i < 10; i += 1)
   alert(i);

// better
for (var i = 0; i < 10; i += 1) {
   alert(i);
}

Similarly for if conditions:
// bad
if (true)
   alert(1);
else
   alert(2);

// better
if (true) {
   alert(1);
} else {
   alert(2);
} 

Opening Brace Location

semicolon insertion mechanism—JavaScript is not picky when you choose not to end your lines properly with a semicolon and adds it for you.

// warning: unexpected return value

function func() {
    return
    {
        name: "Batman"
    };
}

If you expect this function to return an object with a  name property, you’ll be surprised. Because of the implied semicolons, the function returns undefined. The preceding code is equivalent to this one:

// warning: unexpected return value
function func() {
    return undefined;
    // unreachable code follows...
    {
        name: "Batman"
    };
}

In conclusion, always use curly braces and always put the opening one on the same line as the previous statement:

function func() {
    return {
        name: "Batman"
    };
} 

White Space

Good places to use a white space include:

• After the semicolons that separate the parts of a for loop: for example, for (var i= 0; i < 10; i += 1) {...}

• Initializing multiple variables (i and max) in a for loop:  for (var i = 0, max = 10; i < max; i += 1) {...}

• After the commas that delimit array items: var a = [1, 2, 3];

• After commas in object properties and after colons that divide property names and their values: var o = {a: 1, b: 2};

• Delimiting function arguments: myFunc(a, b, c)

• Before the curly braces in function declarations: function myFunc() {}

• After function in anonymous function expressions:  var myFunc = function () {};

 

Another good use for white space is to separate all operators and their operands with

spaces, which basically means use a space before and after  +,  -,  *,  =,  <,  >,  <=,  >=,  = = =,  != =, &&, ||, +=, and so on:

// generous and consistent spacing makes the code easier to read allowing it to "breathe"
var d = 0,
a = b + 1;
if (a && b && c) {
    d = a % c;
    a += d;
}

// antipattern
// missing or inconsistent spaces make the code confusing
var d= 0,
a =b+1;
if (a&& b&&c) {
    d=a %c;
    a+= d;
}

And a final note about white space—curly braces spacing. It’s good to use a space:

• Before opening curly braces ({) in functions,  if-else cases, loops, and object literals

• Between the closing curly brace (}) and else or while