The JavaScript Beginner’s Handbook 2020 Edition

Note that this implies that owners of “parent” namespace groups are necessarily aware of all child namespaces, since they exist in the same directory. Module namespaces may never be named as a direct child of another module’s namespace. Exactly one blank line separates each section that is present, except the file’s implementation, which may be preceded by 1 or 2 blank lines. Other terminology notes will appear occasionally throughout the document. This Style Guide uses RFC 2119 terminology when using the phrases must,must not, should, should not, and may.

What started as a tiny language inside the browser is now the most popular language in the world. Our JavaScript courseComparing Front-End Frameworks can help you make an informed choice. Experiment with each framework, get a feel for how it works, and decide which one is best suited for your project needs or style of programming. W3Schools maintains a complete JavaScript reference, including all HTML and browser objects.

Expressions and operators

Without complicating your learning process with things that are outside of it, and provided by external ecosystems. For example, the console.log() line you can find in many code examples is not JavaScript. Instead, it’s part of the vast library of APIs provided to us in the browser.

The goog.require and goog.requireType statements form a contiguous block with no empty lines. This block follows the goog.module declaration separatedby a single empty line. The entire argument togoog.require or goog.requireType is a namespace defined by a goog.modulein a separate file. Goog.require and goog.requireType statements may not appear anywhere else in the file. You can write JavaScript using an object-oriented paradigm, using prototypes and the new classes syntax. You can write JavaScript in functional programming style, with its first-class functions, or even in an imperative style (C-like). Visibility annotations (@private, @package, @protected) may be specified in a @fileoverview block, or on any exported symbol or property.

Array and object initializers expressions

Goog.require in ES modules works as it does in goog.module files. You can require any Closure namespace symbol (i.e., symbols created by goog.provide orgoog.module) and goog.require will return the value. Do not export container classes or objects with static methods or properties for the sake of namespacing. Classes, enums, functions, constants, and other symbols are exported using theexports object. Exported symbols may be defined directly on the exportsobject, 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 @private nor do their names end with an underscore.

The following switch label returns to the previous indentation level, as if a block had been closed. Line break after the closing brace if that brace terminates a statement or the body of a function or class statement, or a class method. Specifically, there is no line break after the brace if it is followed by else, catch,while, or a comma, semicolon, or right-parenthesis. // goog.require lines must be at the top level before any other code. If a module is imported only for its side effects, the call must be agoog.require (not a goog.requireType) and assignment may be omitted.

Arrays

We just need to pay a bit of attention, even if most of the times those basic scenarios never show up in your code. This is all possible because JavaScript does not strictly require semicolons.

There is no prescribed ordering for exported and module-local symbols. If a variable is defined outside of a function or block, it’s attached to the global object and it has a global scope, which mean it’s available in every part of a program. Compare it to code using promises, or callback functions. There is a special method called constructor() that we can use to initialize the class properties when we create a new object instance. Another way to define strings is to use template literals, defined inside backticks. They are especially useful to make multiline strings much simpler. With single or double quotes you can’t define a multiline string easily – you’d need to use escaping characters.

JS References

Lexical Scoping is a particular kind of scoping where variables of a parent function are made available to inner functions as well. The scope of an inner function also includes the scope of a parent function. Code is asynchronous when you initiate something, forget about it, and when the result is ready you get it back without having to wait for it. Promises and async/await are the modern way to handle async.

If there exist or will exist subclasses, including frameworks that create subclasses, that cannot be immediately changed to use ES6 class syntax. If such a class were to use ES6 syntax, all downstream subclasses not using ES6 class syntax would need to be modified. While Object does not have the same problems as Array, it is still disallowed for consistency. Addresses the discouraged practice of using a variable number of spaces to align certain tokens with previous lines. ES module import and export from statements (see?? and ??). Braces are required for all control structures (i.e. if, else, for, do,while, as well as any others), even if the body contains only a single statement.