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 valuefunction 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