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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>Google JavaScript Style Guide</title>
<link rel="stylesheet" href="javaguide.css" />
<script src="include/styleguide.js"></script>
<link rel="shortcut icon" href="https://www.google.com/favicon.ico" />
<script src="include/jsguide.js"></script>
</head>
<body onload="initStyleGuide();">
<div id="content">
<h1>Google JavaScript Style Guide</h1>
<h2 id="introduction">1 Introduction</h2>
<p>
This document serves as the <strong>complete</strong> definition of
Google’s coding standards for source code in the JavaScript
programming language. A JavaScript source file is described as being
<em>in Google Style</em> if and only if it adheres to the rules herein.
</p>
<p>
Like other programming style guides, the issues covered span not only
aesthetic issues of formatting, but other types of conventions or coding
standards as well. However, this document focuses primarily on the
hard-and-fast rules that we follow universally, and avoids giving advice
that isn't clearly enforceable (whether by human or tool).
</p>
<h3 id="terminology-notes">1.1 Terminology notes</h3>
<p>In this document, unless otherwise clarified:</p>
<ol>
<li>
<p>
The term <em>comment</em> always refers to
<em>implementation</em> comments. We do not use the phrase
<q>documentation comments</q>, instead using the common term
“JSDoc” for both human-readable text and
machine-readable annotations within <code>/** … */</code>.
</p>
</li>
<li>
<p>
This Style Guide uses
<a href="http://tools.ietf.org/html/rfc2119">RFC 2119</a>
terminology when using the phrases <em>must</em>, <em>must not</em>,
<em>should</em>, <em>should not</em>, and <em>may</em>. The terms
<em>prefer</em> and <em>avoid</em> correspond to <em>should</em> and
<em>should not</em>, respectively. Imperative and declarative
statements are prescriptive and correspond to <em>must</em>.
</p>
</li>
</ol>
<p>
Other <q>terminology notes</q> will appear occasionally throughout the
document.
</p>
<h3 id="guide-notes">1.2 Guide notes</h3>
<p>
Example code in this document is <strong>non-normative</strong>. That
is, while the examples are in Google Style, they may not illustrate the
<em>only</em> stylish way to represent the code. Optional formatting
choices made in examples must not be enforced as rules.
</p>
<h2 id="source-file-basics">2 Source file basics</h2>
<h3 id="file-name">2.1 File name</h3>
<p>
File names must be all lowercase and may include underscores
(<code>_</code>) or dashes (<code>-</code>), but no additional
punctuation. Follow the convention that your project uses.
Filenames’ extension must be <code>.js</code>.
</p>
<h3 id="file-encoding">2.2 File encoding: UTF-8</h3>
<p>Source files are encoded in <strong>UTF-8</strong>.</p>
<h3 id="special-characters">2.3 Special characters</h3>
<h4 id="whitespace-characters">2.3.1 Whitespace characters</h4>
<p>
Aside from the line terminator sequence, the ASCII horizontal space
character (0x20) is the only whitespace character that appears anywhere
in a source file. This implies that
</p>
<ol>
<li>
<p>
All other whitespace characters in string literals are escaped, and
</p>
</li>
<li>
<p>Tab characters are <strong>not</strong> used for indentation.</p>
</li>
</ol>
<h4 id="special-escape-sequences">2.3.2 Special escape sequences</h4>
<p>
For any character that has a special escape sequence (<code>\'</code>,
<code>\"</code>, <code>\\</code>, <code>\b</code>, <code>\f</code>,
<code>\n</code>, <code>\r</code>, <code>\t</code>, <code>\v</code>),
that sequence is used rather than the corresponding numeric escape (e.g
<code>\x0a</code>, <code>\u000a</code>, or <code>\u{a}</code>). Legacy
octal escapes are never used.
</p>
<h4 id="non-ascii-characters">2.3.3 Non-ASCII characters</h4>
<p>
For the remaining non-ASCII characters, either the actual Unicode
character (e.g. <code>∞</code>) or the equivalent hex or Unicode
escape (e.g. <code>\u221e</code>) is used, depending only on which makes
the code <strong>easier to read and understand</strong>.
</p>
<p>
Tip: In the Unicode escape case, and occasionally even when actual
Unicode characters are used, an explanatory comment can be very helpful.
</p>
<pre><code class="language-js prettyprint">/* Best: perfectly clear even without a comment. */
const units = 'μs';
/* Allowed: but unnecessary as μ is a printable character. */
const units = '\u03bcs'; // 'μs'
/* Good: use escapes for non-printable characters with a comment for clarity. */
return '\ufeff' + content; // Prepend a byte order mark.
</code></pre>
<pre><code class="language-js prettyprint badcode">/* Poor: the reader has no idea what character this is. */
const units = '\u03bcs';
</code></pre>
<p>
Tip: Never make your code less readable simply out of fear that some
programs might not handle non-ASCII characters properly. If that
happens, those programs are <strong>broken</strong> and they must be
<strong>fixed</strong>.
</p>
<h2 id="source-file-structure">3 Source file structure</h2>
<p>
All new source files should either be a <code>goog.module</code> file (a
file containing a <code>goog.module</code> call) or an ECMAScript (ES)
module (uses <code>import</code> and <code>export</code> statements).
Files consist of the following, <strong>in order</strong>:
</p>
<ol>
<li>License or copyright information, if present</li>
<li><code>@fileoverview</code> JSDoc, if present</li>
<li>
<code>goog.module</code> statement, if a <code>goog.module</code> file
</li>
<li>ES <code>import</code> statements, if an ES module</li>
<li>
<code>goog.require</code> and <code>goog.requireType</code> statements
</li>
<li>The file’s implementation</li>
</ol>
<p>
<strong>Exactly one blank line</strong> separates each section that is
present, except the file's implementation, which may be preceded by 1 or
2 blank lines.
</p>
<h3 id="file-copyright">
3.1 License or copyright information, if present
</h3>
<p>
If license or copyright information belongs in a file, it belongs here.
</p>
<h3 id="file-fileoverview">
3.2 <code>@fileoverview</code> JSDoc, if present
</h3>
<p>
See <a href="#jsdoc-top-file-level-comments">??</a> for formatting
rules.
</p>
<h3 id="file-goog-module">3.3 <code>goog.module</code> statement</h3>
<p>
All <code>goog.module</code> files must declare exactly one
<code>goog.module</code> name on a single line: lines containing a
<code>goog.module</code> declaration must not be wrapped, and are
therefore an exception to the 80-column limit.
</p>
<p>
The entire argument to goog.module is what defines a namespace. It is
the package name (an identifier that reflects the fragment of the
directory structure where the code lives) plus, optionally, the main
class/enum/interface that it defines concatenated to the end.
</p>
<p>Example</p>
<pre><code class="language-js prettyprint">goog.module('search.urlHistory.UrlHistoryService');
</code></pre>
<h4 id="naming-hierarchy">3.3.1 Hierarchy</h4>
<p>
Module namespaces may never be named as a <em>direct</em> child of
another module's namespace.
</p>
<p>Disallowed:</p>
<pre><code class="language-js prettyprint badcode">goog.module('foo.bar'); // 'foo.bar.qux' would be fine, though
goog.module('foo.bar.baz');
</code></pre>
<p>
The directory hierarchy reflects the namespace hierarchy, so that
deeper-nested children are subdirectories of higher-level parent
directories. Note that this implies that owners of “parent”
namespace groups are necessarily aware of all child namespaces, since
they exist in the same directory.
</p>
<h4 id="file-declare-legacy-namespace">
3.3.2 <code>goog.module.declareLegacyNamespace</code>
</h4>
<p>
The single <code>goog.module</code> statement may optionally be followed
by a call to <code>goog.module.declareLegacyNamespace();</code>. Avoid
<code>goog.module.declareLegacyNamespace()</code> when possible.
</p>
<p>Example:</p>
<pre><code class="language-js prettyprint">goog.module('my.test.helpers');
goog.module.declareLegacyNamespace();
goog.setTestOnly();
</code></pre>
<p>
<code>goog.module.declareLegacyNamespace</code> exists to ease the
transition from traditional object hierarchy-based namespaces but comes
with some naming restrictions. As the child module name must be created
after the parent namespace, this name <strong>must not</strong> be a
child or parent of any other <code>goog.module</code> (for example,
<code>goog.module('parent');</code> and
<code>goog.module('parent.child');</code> cannot both exist safely, nor
can <code>goog.module('parent');</code> and
<code>goog.module('parent.child.grandchild');</code>).
</p>
<h3 id="file-goog-module-exports">
3.3.3 <code>goog.module</code> Exports
</h3>
<p>
Classes, enums, functions, constants, and other symbols are exported
using the <code>exports</code> object. Exported symbols may be defined
directly on the <code>exports</code> object, or else declared locally
and exported separately. Symbols are only exported if they are meant to
be used outside the module. Non-exported module-local symbols are not
declared <code>@private</code> nor do their names end with an
underscore. There is no prescribed ordering for exported and
module-local symbols.
</p>
<p>Examples:</p>
<pre><code class="language-js prettyprint">const /** !Array<number> */ exportedArray = [1, 2, 3];
const /** !Array<number> */ moduleLocalArray = [4, 5, 6];
/** @return {number} */
function moduleLocalFunction() {
return moduleLocalArray.length;
}
/** @return {number} */
function exportedFunction() {
return moduleLocalFunction() * 2;
}
exports = {exportedArray, exportedFunction};
</code></pre>
<pre><code class="language-js prettyprint">/** @const {number} */
exports.CONSTANT_ONE = 1;
/** @const {string} */
exports.CONSTANT_TWO = 'Another constant';
</code></pre>
<p>
Do not annotate the <code>exports</code> object as
<code>@const</code> as it is already treated as a constant by the
compiler.
</p>
<pre><code class="language-js badcode prettyprint">/** @const */
exports = {exportedFunction};
</code></pre>
<p><span id="file-es6-modules"></span></p>
<h3 id="file-es-modules">3.4 ES modules</h3>
<p><span id="es6-module-imports"></span></p>
<h4 id="es-module-imports">3.4.1 Imports</h4>
<p>
Import statements must not be line wrapped and are therefore an
exception to the 80-column limit.
</p>
<p><span id="es6-import-paths"></span></p>
<h5 id="esm-import-paths">3.4.1.1 Import paths</h5>
<p>
ES module files must use the <code>import</code> statement to import
other ES module files. Do not <code>goog.require</code> another ES
module.
</p>
<pre><code class="language-js prettyprint external">import './sideeffects.js';
import * as goog from '../closure/goog/goog.js';
import * as parent from '../parent.js';
import {name} from './sibling.js';
</code></pre>
<p><span id="es6-import-paths-file-extension"></span></p>
<h6 id="esm-import-paths-file-extension">
3.4.1.1.1 File extensions in import paths
</h6>
<p>
The <code>.js</code> file extension is not optional in import paths and
must always be included.
</p>
<pre><code class="language-js badcode prettyprint">import '../directory/file';
</code></pre>
<pre><code class="language-js good prettyprint">import '../directory/file.js';
</code></pre>
<h5 id="importing-the-same-file-multiple-times">
3.4.1.2 Importing the same file multiple times
</h5>
<p>
Do not import the same file multiple times. This can make it hard to
determine the aggregate imports of a file.
</p>
<pre><code class="language-js badcode prettyprint">// Imports have the same path, but since it doesn't align it can be hard to see.
import {short} from './long/path/to/a/file.js';
import {aLongNameThatBreaksAlignment} from './long/path/to/a/file.js';
</code></pre>
<p><span id="naming-es6-imports"></span></p>
<h5 id="naming-esm-imports">3.4.1.3 Naming imports</h5>
<h6 id="naming-module-imports">3.4.1.3.1 Naming module imports</h6>
<p>
Module import names (<code>import * as name</code>) are
<code>lowerCamelCase</code> names that are derived from the imported
file name.
</p>
<pre><code class="language-js prettyprint">import * as fileOne from '../file-one.js';
import * as fileTwo from '../file_two.js';
import * as fileThree from '../filethree.js';
</code></pre>
<pre><code class="language-js prettyprint">import * as libString from './lib/string.js';
import * as math from './math/math.js';
import * as vectorMath from './vector/math.js';
</code></pre>
<h6 id="naming-default-imports">3.4.1.3.2 Naming default imports</h6>
<p>
Default import names are derived from the imported file name and follow
the rules in <a href="#naming-rules-by-identifier-type">??</a>.
</p>
<pre><code class="language-js prettyprint">import MyClass from '../my-class.js';
import myFunction from '../my_function.js';
import SOME_CONSTANT from '../someconstant.js';
</code></pre>
<p>
Note: In general this should not happen as default exports are banned by
this style guide, see <a href="#named-vs-default-exports">??</a>.
Default imports are only used to import modules that do not conform to
this style guide.
</p>
<h6 id="naming-named-imports">3.4.1.3.3 Naming named imports</h6>
<p>
In general symbols imported via the named import (<code
>import {name}</code
>) should keep the same name. Avoid aliasing imports (<code
>import {SomeThing as SomeOtherThing}</code
>). Prefer fixing name collisions by using a module import (<code
>import *</code
>) or renaming the exports themselves.
</p>
<pre><code class="language-js prettyprint">import * as bigAnimals from './biganimals.js';
import * as domesticatedAnimals from './domesticatedanimals.js';
new bigAnimals.Cat();
new domesticatedAnimals.Cat();
</code></pre>
<p>
If renaming a named import is needed then use components of the imported
module's file name or path in the resulting alias.
</p>
<pre><code class="language-js prettyprint">import {Cat as BigCat} from './biganimals.js';
import {Cat as DomesticatedCat} from './domesticatedanimals.js';
new BigCat();
new DomesticatedCat();
</code></pre>
<p><span id="es6-module-exports"></span></p>
<h4 id="es-module-exports">3.4.2 Exports</h4>
<p>
Symbols are only exported if they are meant to be used outside the
module. Non-exported module-local symbols are not declared
<code>@private</code> nor do their names end with an underscore. There
is no prescribed ordering for exported and module-local symbols.
</p>
<h5 id="named-vs-default-exports">3.4.2.1 Named vs default exports</h5>
<p>
Use named exports in all code. You can apply the
<code>export</code> keyword to a declaration, or use the
<code>export {name};</code> syntax.
</p>
<p>
Do not use default exports. Importing modules must give a name to these
values, which can lead to inconsistencies in naming across modules.
</p>
<pre><code class="language-js badcode prettyprint">// Do not use default exports:
export default class Foo { ... } // BAD!
</code></pre>
<pre><code class="language-js good prettyprint">// Use named exports:
export class Foo { ... }
</code></pre>
<pre><code class="language-js good prettyprint">// Alternate style named exports:
class Foo { ... }
export {Foo};
</code></pre>
<h5 id="exporting-static-containers">
3.4.2.2 Exporting static container classes and objects
</h5>
<p>
Do not export container classes or objects with static methods or
properties for the sake of namespacing.
</p>
<pre><code class="language-js badcode prettyprint">// container.js
// Bad: Container is an exported class that has only static methods and fields.
export class Container {
/** @return {number} */
static bar() {
return 1;
}
}
/** @const {number} */
Container.FOO = 1;
</code></pre>
<p>Instead, export individual constants and functions:</p>
<pre><code class="language-js good prettyprint">/** @return {number} */
export function bar() {
return 1;
}
export const /** number */ FOO = 1;
</code></pre>
<p><span id="es6-exports-mutability"></span></p>
<h5 id="esm-exports-mutability">3.4.2.3 Mutability of exports</h5>
<p>
Exported variables must not be mutated outside of module initialization.
</p>
<p>
There are alternatives if mutation is needed, including exporting a
constant reference to an object that has mutable fields or exporting
accessor functions for mutable data.
</p>
<pre><code class="language-js badcode prettyprint">// Bad: both foo and mutateFoo are exported and mutated.
export let /** number */ foo = 0;
/**
* Mutates foo.
*/
export function mutateFoo() {
++foo;
}
/**
* @param {function(number): number} newMutateFoo
*/
export function setMutateFoo(newMutateFoo) {
// Exported classes and functions can be mutated!
mutateFoo = () => {
foo = newMutateFoo(foo);
};
}
</code></pre>
<pre><code class="language-js good prettyprint">// Good: Rather than export the mutable variables foo and mutateFoo directly,
// instead make them module scoped and export a getter for foo and a wrapper for
// mutateFooFunc.
let /** number */ foo = 0;
let /** function(number): number */ mutateFooFunc = foo => foo + 1;
/** @return {number} */
export function getFoo() {
return foo;
}
export function mutateFoo() {
foo = mutateFooFunc(foo);
}
/** @param {function(number): number} mutateFoo */
export function setMutateFoo(mutateFoo) {
mutateFooFunc = mutateFoo;
}
</code></pre>
<p><span id="es6-module-circular-dependencies"></span></p>
<h5 id="es-module-export-from">3.4.2.4 export from</h5>
<p>
<code>export from</code> statements must not be line wrapped and are
therefore an exception to the 80-column limit. This applies to both
<code>export from</code> flavors.
</p>
<pre><code class="language-js">export {specificName} from './other.js';
export * from './another.js';
</code></pre>
<h4 id="es-module-circular-dependencies">
3.4.3 Circular Dependencies in ES modules
</h4>
<p>
Do not create cycles between ES modules, even though the ECMAScript
specification allows this. Note that it is possible to create cycles
with both the <code>import</code> and <code>export</code> statements.
</p>
<pre><code class="language-js badcode prettyprint">// a.js
import './b.js';
</code></pre>
<pre><code class="language-js badcode prettyprint">// b.js
import './a.js';
// `export from` can cause circular dependencies too!
export {x} from './c.js';
</code></pre>
<pre><code class="language-js badcode prettyprint">// c.js
import './b.js';
export let x;
</code></pre>
<p><span id="es6-module-closure-interop"></span></p>
<h4 id="es-module-closure-interop">3.4.4 Interoperating with Closure</h4>
<p><span id="es6-module-referencing-goog"></span></p>
<h5 id="es-module-referencing-goog">3.4.4.1 Referencing goog</h5>
<p>
To reference the Closure <code>goog</code> namespace, import Closure's
<code>goog.js</code>.
</p>
<pre><code class="language-js good prettyprint external">import * as goog from '../closure/goog/goog.js';
const name = goog.require('a.name');
export const CONSTANT = name.compute();
</code></pre>
<p>
<code>goog.js</code> exports only a subset of properties from the global
<code>goog</code> that can be used in ES modules.
</p>
<p><span id="goog-require-in-es6-module"></span></p>
<h5 id="goog-require-in-es-module">3.4.4.2 goog.require in ES modules</h5>
<p>
<code>goog.require</code> in ES modules works as it does in
<code>goog.module</code> files. You can require any Closure namespace
symbol (i.e., symbols created by <code>goog.provide</code> or
<code>goog.module</code>) and <code>goog.require</code> will return the
value.
</p>
<pre><code class="language-js prettyprint external">import * as goog from '../closure/goog/goog.js';
import * as anEsModule from './anEsModule.js';
const GoogPromise = goog.require('goog.Promise');
const myNamespace = goog.require('my.namespace');
</code></pre>
<p><span id="closure-module-id-in-es6-module"></span></p>
<h5 id="closure-module-id-in-es-module">
3.4.4.3 Declaring Closure Module IDs in ES modules
</h5>
<p>
<code>goog.declareModuleId</code> can be used within ES modules to
declare a <code>goog.module</code>-like module ID. This means that this
module ID can be <code>goog.require</code>d,
<code>goog.module.get</code>d, <code>goog.forwardDeclare</code>'d, etc.
as if it were a <code>goog.module</code> that did not call
<code>goog.module.declareLegacyNamespace</code>. It does not create the
module ID as a globally available JavaScript symbol.
</p>
<p>
A <code>goog.require</code> (or <code>goog.module.get</code>) for a
module ID from <code>goog.declareModuleId</code> will always return the
module object (as if it was <code>import *</code>'d). As a result, the
argument to <code>goog.declareModuleId</code> should always end with a
<code>lowerCamelCaseName</code>.
</p>
<p>
Note: It is an error to call
<code>goog.module.declareLegacyNamespace</code> in an ES module, it can
only be called from <code>goog.module</code> files. There is no direct
way to associate a <q>legacy</q> namespace with an ES module.
</p>
<p>
<code>goog.declareModuleId</code> should only be used to upgrade Closure
files to ES modules in place, where named exports are used.
</p>
<pre><code class="language-js prettyprint external">import * as goog from '../closure/goog.js';
goog.declareModuleId('my.esm');
export class Class {};
</code></pre>
<h3 id="file-set-test-only">3.5 <code>goog.setTestOnly</code></h3>
<p>
In a <code>goog.module</code> file the
<code>goog.module</code> statement may optionally be followed by a call
to <code>goog.setTestOnly()</code>.
</p>
<p>
In an ES module the <code>import</code> statements may optionally be
followed by a call to <code>goog.setTestOnly()</code>.
</p>
<h3 id="file-goog-require">
3.6 <code>goog.require</code> and
<code>goog.requireType</code> statements
</h3>
<p>
Imports are done with <code>goog.require</code> and
<code>goog.requireType</code> statements. The names imported by a
<code>goog.require</code> statement may be used both in code and in type
annotations, while those imported by a <code>goog.requireType</code> may
be used in type annotations only.
</p>
<p>
The <code>goog.require</code> and
<code>goog.requireType</code> statements form a contiguous block with no
empty lines. This block follows the <code>goog.module</code> declaration
separated <a href="#source-file-structure">by a single empty line</a>.
The entire argument to <code>goog.require</code> or
<code>goog.requireType</code> is a namespace defined by a
<code>goog.module</code> in a separate file.
<code>goog.require</code> and <code>goog.requireType</code> statements
may not appear anywhere else in the file.
</p>
<p>
Each <code>goog.require</code> or <code>goog.requireType</code> is
assigned to a single constant alias, or else destructured into several
constant aliases. These aliases are the only acceptable way to refer to
dependencies in type annotations or code. Fully qualified namespaces
must not be used anywhere, except as an argument to
<code>goog.require</code> or <code>goog.requireType</code>.
</p>
<p>
<strong>Exception</strong>: Types, variables, and functions declared in
externs files have to use their fully qualified name in type annotations
and code.
</p>
<p>
Aliases must match the final dot-separated component of the imported
module's namespace.
</p>
<p>
<strong>Exception</strong>: In certain cases, additional components of
the namespace can be used to form a longer alias. The resulting alias
must retain the original identifier's casing such that it still
correctly identifies its type. Longer aliases may be used to
disambiguate otherwise identical aliases, or if it significantly
improves readability. In addition, a longer alias must be used to
prevent masking native types such as <code>Element</code>,
<code>Event</code>, <code>Error</code>, <code>Map</code>, and
<code>Promise</code> (for a more complete list, see
<a
href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects"
>Standard Built-in Objects</a
>
and
<a href="https://developer.mozilla.org/en-US/docs/Web/API">Web APIs</a>
at MDN). When renaming destructured aliases, a space must follow the
colon as required in <a href="#formatting-horizontal-whitespace">??</a>.
</p>
<p>
A file should not contain both a <code>goog.require</code> and a
<code>goog.requireType</code> statement for the same namespace. If the
imported name is used both in code and in type annotations, it should be
imported by a single <code>goog.require</code> statement.
</p>
<p>
If a module is imported only for its side effects, the call must be a
<code>goog.require</code> (not a <code>goog.requireType</code>) and
assignment may be omitted. A comment is required to explain why this is
needed and suppress a compiler warning.
</p>
<p>
The lines are sorted according to the following rules: All requires with
a name on the left hand side come first, sorted alphabetically by those
names. Then destructuring requires, again sorted by the names on the
left hand side. Finally, any require calls that are standalone
(generally these are for modules imported just for their side effects).
</p>
<p>
Tip: There’s no need to memorize this order and enforce it
manually. You can rely on your IDE to report requires that are not
sorted correctly.
</p>
<p>
If a long alias or module name would cause a line to exceed the
80-column limit, it <strong>must not</strong> be wrapped: require lines
are an exception to the 80-column limit.
</p>
<p>Example:</p>
<pre><code class="language-js prettyprint">// Standard alias style.
const MyClass = goog.require('some.package.MyClass');
const MyType = goog.requireType('some.package.MyType');
// Namespace-based alias used to disambiguate.
const NsMyClass = goog.require('other.ns.MyClass');
// Namespace-based alias used to prevent masking native type.
const RendererElement = goog.require('web.renderer.Element');
// Out of sequence namespace-based aliases used to improve readability.
// Also, require lines longer than 80 columns must not be wrapped.
const SomeDataStructureModel = goog.requireType('identical.package.identifiers.models.SomeDataStructure');
const SomeDataStructureProto = goog.require('proto.identical.package.identifiers.SomeDataStructure');
// Standard alias style.
const asserts = goog.require('goog.asserts');
// Namespace-based alias used to disambiguate.
const testingAsserts = goog.require('goog.testing.asserts');
// Standard destructuring into aliases.
const {clear, clone} = goog.require('goog.array');
const {Rgb} = goog.require('goog.color');
// Namespace-based destructuring into aliases in order to disambiguate.
const {SomeType: FooSomeType} = goog.requireType('foo.types');
const {clear: objectClear, clone: objectClone} = goog.require('goog.object');
// goog.require without an alias in order to trigger side effects.
/** @suppress {extraRequire} Initializes MyFramework. */
goog.require('my.framework.initialization');
</code></pre>
<p>Discouraged:</p>
<pre><code class="language-js badcode prettyprint">// If necessary to disambiguate, prefer PackageClass over SomeClass as it is
// closer to the format of the module name.
const SomeClass = goog.require('some.package.Class');
</code></pre>
<p>Disallowed:</p>
<pre><code class="language-js badcode prettyprint">// Extra terms must come from the namespace.
const MyClassForBizzing = goog.require('some.package.MyClass');
// Alias must include the entire final namespace component.
const MyClass = goog.require('some.package.MyClassForBizzing');
// Alias must not mask native type (should be `const JspbMap` here).
const Map = goog.require('jspb.Map');
// Don't break goog.require lines over 80 columns.
const SomeDataStructure =
goog.require('proto.identical.package.identifiers.SomeDataStructure');
// Alias must be based on the namespace.
const randomName = goog.require('something.else');
// Missing a space after the colon.
const {Foo:FooProto} = goog.require('some.package.proto.Foo');
// goog.requireType without an alias.
goog.requireType('some.package.with.a.Type');
/**
* @param {!some.unimported.Dependency} param All external types used in JSDoc
* annotations must be goog.require'd, unless declared in externs.
*/
function someFunction(param) {
// goog.require lines must be at the top level before any other code.
const alias = goog.require('my.long.name.alias');
// ...
}
</code></pre>
<h3 id="file-implementation">3.7 The file’s implementation</h3>
<p>
The actual implementation follows after all dependency information is
declared (separated by at least one blank line).
</p>
<p>
This may consist of any module-local declarations (constants, variables,
classes, functions, etc), as well as any exported symbols.
</p>
<h2 id="formatting">4 Formatting</h2>
<p>
<strong>Terminology Note</strong>: <em>block-like construct</em> refers
to the body of a class, function, method, or brace-delimited block of
code. Note that, by <a href="#features-array-literals">??</a> and
<a href="#features-object-literals">??</a>, any array or object literal
may optionally be treated as if it were a block-like construct.
</p>
<p>
Tip: Use <code>clang-format</code>. The JavaScript community has
invested effort to make sure clang-format <q>does the right thing</q> on
JavaScript files. <code>clang-format</code> has integration with several
popular editors.
</p>
<h3 id="formatting-braces">4.1 Braces</h3>
<h4 id="formatting-braces-all">
4.1.1 Braces are used for all control structures
</h4>
<p>
Braces are required for all control structures (i.e. <code>if</code>,
<code>else</code>, <code>for</code>, <code>do</code>,
<code>while</code>, as well as any others), even if the body contains
only a single statement. The first statement of a non-empty block must
begin on its own line.
</p>
<p>Disallowed:</p>
<pre><code class="language-js badcode prettyprint">if (someVeryLongCondition())
doSomething();
for (let i = 0; i < foo.length; i++) bar(foo[i]);
</code></pre>
<p>
<strong>Exception</strong>: A simple if statement that can fit entirely
on a single line with no wrapping (and that doesn’t have an else)
may be kept on a single line with no braces when it improves
readability. This is the only case in which a control structure may omit
braces and newlines.
</p>
<pre><code class="language-js prettyprint">if (shortCondition()) foo();
</code></pre>
<h4 id="formatting-nonempty-blocks">
4.1.2 Nonempty blocks: K&R style
</h4>
<p>
Braces follow the Kernighan and Ritchie style (<q
><a
href="http://www.codinghorror.com/blog/2012/07/new-programming-jargon.html"
>Egyptian brackets</a
></q
>) for <em>nonempty</em> blocks and block-like constructs:
</p>
<ul>
<li>No line break before the opening brace.</li>
<li>Line break after the opening brace.</li>
<li>Line break before the closing brace.</li>
<li>
Line break after the closing brace <em>if</em> that brace terminates a
statement or the body of a function or class statement, or a class
method. Specifically, there is <em>no</em> line break after the brace
if it is followed by <code>else</code>, <code>catch</code>,
<code>while</code>, or a comma, semicolon, or right-parenthesis.
</li>
</ul>
<p>Example:</p>
<pre><code class="language-js prettyprint">class InnerClass {
constructor() {}
/** @param {number} foo */
method(foo) {
if (condition(foo)) {
try {
// Note: this might fail.
something();
} catch (err) {
recover();
}
}
}
}
</code></pre>
<h4 id="formatting-empty-blocks">4.1.3 Empty blocks: may be concise</h4>
<p>
An empty block or block-like construct <em>may</em> be closed
immediately after it is opened, with no characters, space, or line break
in between (i.e. <code>{}</code>), <strong>unless</strong> it is a part
of a <em>multi-block statement</em> (one that directly contains multiple
blocks: <code>if</code>/<code>else</code> or