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Unethical JSJS Misconceptions and Errors
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@giorgionatili
On paper, Giorgio Natili is an engineering lead at Akamai Technologies where he spearheads the implementation of the new web apps for the security products line of AkamaiOn the job, Giorgio is a strong proponent of agile development practices whose passion for usable, maintainable and testable code is only surpassed by his determination to make things work.
@giorgionatiliUnethical JavaScript3
Agenda
Review the knowledge base that is behind this presentation
Definitions
� An overview of the hidden gems of JavaScript and V8
Misconceptions
�
A couple of recommendations to write effective and maintainable JavaScript
Conclusions
�An overview of effective plain JavaScript code style and techniques
Ethical JavaScript
�
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IntroUnethical, maintainable and readable are three important adjectives, let’s review them in the context of JavaScript
�
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Topics
General definition and how it is applicable to the context of JavaScript
Unethical
U The main principles of maintainable code, and how to apply them in JavaScript
Maintainable Code
M Readable code is the main key to write scalable softwares
Readability
R
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Unethical
Lacking moral principles; unwilling to adhere to proper rules of conduct
General Definition�
Not conforming to approved standards of social or professional behavior
More in Context�
Corrupt, illegal, improper, unfair, unprofessional, unscrupulous, wrong, etc.
Synonyms�
Which is the first step to make JavaScript Ethical?
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Maintainable Code
Code should not be rigid and not easy to change, even more, changes should be predictable
Not Rigid�
Maintainability is inversely proportional to the amount of time it takes a developer to make a change and the risk that change will break something
Measurable �
At the heart of maintainability is carefully constructed code that is easy to read
Long Story Short�
@giorgionatiliUnethical JavaScript9
Readability Principles
Give your objects and methods names that truly reflect the concept they are modeling, any nontechnical member of the team should be able to understand the object
Intention-Revealing Interfaces�
Calling a function should have a single outcome that is predictable due to the object’s Intention-Revealing Interface
Side-Effect-Free Functions �
Avoid to modify the same data structures from different parts of the code, try to minimize race conditions
Immutability �
Standalone objects are ideal because they are not coupled to any other code and they can be understood in isolation
Standalone Objects�
@giorgionatiliUnethical JavaScript10
Unreadable Code
const getAction = (newPayload, isRejected) => ({ type: `${type}_${isRejected ? REJECTED : FULFILLED}`, ...newPayload ? { payload: newPayload } : {}, ...!!meta ? { meta } : {}, ...isRejected ? { error: true } : {} });
Please, Meet the Maintainer
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More Readable
const getAction = (newPayload, isRejected) => ({ type: `${type}_${isRejected ? REJECTED : FULFILLED}`, ...( newPayload ? { payload: newPayload } : {} ), ...( !!meta ? { meta } : {} ), ...( isRejected ? { error: true } : {} ) });
Know your enemy and you can fight a hundred battles without disaster Breath…
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Inconsistency JavaScript is inconsistent by default, it’s one of the most misunderstood languages and it wasn't designed with the goal of being one of the most diffused programming language
�
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Topics
JavaScript is a language designed in few days and with different goals, hereby there are design flaws
Design Flaws
D The dynamic nature of the language creates interesting side effects when types get converted
Types Conversion
T A deep dive into one of the most ambiguous “data type” ever invented
Truthy & Falsy
W
Operator overloading can be dangerous, the + operator in JavaScript is a clear demonstration
The Plus (+) Operator
P How the value of the this keyword changes, it is a reference to the object that “owns” the executing code
Execution Context
EDifferences, similarities and gotchas of the two most important JavaScript’s data structures
Objects & Arrays
O
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Design Flaws
If someone forgets to declare a variable as local before using it, subtle gremlins can pop up in a program
Variables are global unless declared local�
Types are coerced unexpectedly by smart and fast run times
Messy Type Handling�
Null belongs to a kind of object [Object], mean the object is empty; undefined is a data type, that is not defined
null and undefined�
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Type Conversion
Type conversion behaves differently according to the type the interpreter is expecting and to the operator in the expression
Automatic Type Conversion
�
Most arithmetic operators in Javascript convert their arguments to numbers, the exception is the plus operator
Addictive Overload�
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Conversion Madness
let pi = Math.PI, str = ""+ pi, // to string int = ~~pi, // to integer float = 1 * str, // to float bool = !!pi, // to boolean
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Truthy & Falsy
Like most computer languages, JavaScript supports Boolean data types
Boolean Data Types�
In addition, everything in JavaScript has an inherent Boolean value, generally known as either truthy or falsy
JavaScript Madeness �
When a value is truthy or falsy in JavaScript, it doesn’t mean that the value is true or false; it means that the value coerces to true or false when evaluated in a boolean context
Practically Speaking�
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Falsy Values
false void 0 (zero) "" (empty string) null undefined NaN
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Comparing Falsy Values
false == 0; // true false == ""; // true 0 == ""; // true null == false; // false null == null; // true undefined == undefined; // true undefined == null; // true NaN == null; // false NaN == NaN; // false
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The Falsehood of false
let hello = (value) => {
if (!value) { return `Bye ${value}`; } return `Hi ${value}`; }
hello(false); // 'Bye false' hello(null); // 'Bye null' hello([]); // 'Hi ' hello(new Boolean(false)); // 'Hi false'
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Say it again, please…
Write safer code by using the strict comparison operator (===)
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The Plus (+) Operator
This operator is used to concatenate strings or sum the numbers
Concatenate and Sum�
Considering that only strings and numbers can be added, the runtime apply data type conversions to keep the values around the operator consistent
Automatic Conversion�
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Automatic Conversion
let a = "12";
+a; // -> Number(a) -> 12 a + "hello"; // -> String(a) + "hello" -> 12hello "hello" + a; // -> "hello" + String(b) a + 6; // -> Number(a) + 6 6 + a; // -> 6 + Number(b)
let b = "wtf"; a + b; // -> ToPrimitive(a) + ToPrimitive(b) -> 12wtf
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ToPrimitive
ToPrimitive(input, PreferredType?)
• If input is primitive, return it as is
• Otherwise, if input is an object, calls obj.valueOf(); if the result is
primitive, return it
• Otherwise, call obj.toString(); if the result is a primitive, return it
• Otherwise, throw a TypeError
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Unexpected Behavior
[] + []; // -> '' [] + {}; // -> '[object Object]' {} + {}; // -> NaN {} + []; // -> 0 [1, 3, 5] + 1; // -> "1,3,51" 10 + true; // -> 11 8 + null; // -> 8 12 + undefined; // -> NaN
@giorgionatiliUnethical JavaScript29
Where is this?
let obj = { name: 'giorgio', sayHi: function(msg) { console.log(`Hi, I'm ${this.name}`, msg); } }, otherObject = { name: 'mario' }; let speak = obj.sayHi;
speak('nice to meet you'); // -> Hi, I'm nice to meet you speak.call(otherObject, 'nice to meet you'); // -> Hi, I'm mario nice to meet you speak.apply(obj, ['nice to meet you']); // -> Hi, I'm giorgio nice to meet you
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Object and Array
Every object in JavaScript is an associative array whose keys are strings; when an object other than a string is used as a key in JavaScript, no error occurs
Objects are Associative Arrays�
Arrays are a type of object (off course!) for storing multiple values in a single variable where each value gets numeric index
Arrays�
Array-like objects look like arrays, they have various numbered elements and a length property; but that’s where the similarity stops (aka document.forms)
Array-like Objects�
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Unexpected Behavior
let foo = new Object(); let bar = new Object; let map = {};
map[foo] = "foo"; map[bar] = "bar";
console.log(map[foo]); // -> "bar"
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WTF ?!?
Do you not destroy your enemies when you make them your friends?
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Plain JavaScriptAn overview of data structures, loops, execution context and hidden gems of JavaScript and its runtimes
�
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Topics
Implementing hash tables in JavaScript using ES6 API
Hash Tables
H Exploring the nasty truth about Arrays in JavaScript
Arrays
A Gotchas and improvements of loops in JavaScript
Loops
L
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Hash Tables
In JavaScript, all non-scalar objects behave as associative arrays; the object can use other objects or strings as keys
Hash Tables in JavaScript�
The truth is that hash tables don’t exist in JavaScript because an object by default inherits the methods of the Object data type
Inheritance Issue�
Creating an object with a null prototype is a solution to mitigate the inheritance issue
Mitigation�
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Objects Based Hash Tables
let hash = {}; hash['name'] = 'giorgio'; hash['surname'] = 'natili';
for(let i in hash) { console.log(`${i} ${hash[i]}`); }
console.log(typeof hash); // -> object console.log(hash.hasOwnProperty('surname')); // -> true console.log(!!hash['surname']); // -> true
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ES6 Hash Tables (Map)
let map = new Map() map.set('name', 'giorgio'); map.set('surname', 'natili');
map.forEach((item) => { console.log(item); })
console.log(map.get('name')); // -> giorgio console.log(map.get('surname')); // -> natili
Wait a minute, are you forgetting about Set?
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ES6 Hash Tables (Set)
let set = new Set(['giorgio', 'natili']) .add(42);
for (let x of set) { console.log(x); }
Jenniffer W. DoeMinimal X Template41
Map & Set
There is a strong symmetry between Map and Set, but these data structures should be used in the right scenario
Same same, but different
� Map and Set constructors and methods are both chainable
Chainable
�
Both Map and Set are available in a weak flavor that facilitate garbage collection and prevent potential memory leaks
Weak Collections
�Both Map and Set get designed with the iteration use case in mind, the entries() and values() methods represent the standard way to iterate over collections
Iterable
�
Hash Tables still not exist, but at least collections are predictable
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Arrays
In JavaScript, there isn’t an Array datatype, the result of the comparison typeof [] == 'object' is true
Existence
�
The numeric keys used to access the elements of an Array are strings
Keys�
The length property is not read only, by incrementing or decrementing it, you actually change the data structure
Length�
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Array Length
let data = ['First', 'Second', 'Third']; console.log(data.length, data); // -> 3, ["First", "Second", "Third"]
data.length--; console.log(data.length, data); // -> 2, ["First", "Second"]
data.length++; console.log(data.length, data); // -> 3, ["First", "Second", undefined]
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Looping and Iterating
The for-in statement by itself is not a "bad practice", however it can be mis-used, for example, to iterate over arrays or array-like objects data rather than on their properties
Looping Over Properties�
The for-of is the most concise, direct syntax for looping through array and array-like objects elements; it avoids all the pitfalls of for–in and works with break, continue, and return
Looping Over Data�
The map(), filter(), and reduce() methods are a key element to get a cleaner syntax to filter data structures
Mapping and Filtering�
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The for-in & for-of
let array = ['First', 'Second', 'Third']; array.name = "Cool!";
for (let p in array) { console.log(p); // -> 0, 1, 2, name } for (let p of array) { console.log(p); // -> "First", "Second", "Third" }
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Not so bad
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Poor NamingPoor naming is a cross language issue, anyway, JavaScript dynamic nature deeply influence naming conventions.
�
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Topics
Poor variable names are one of the root causes of bugs and regressions
Variables
V A function is an action, poor function names make your code difficult to understand
Functions
F Classes try to group traits and behaviors of a software, poor naming brings to unmaintainable models
Classes
C
Modules are another tool to group reusable code, poor modules naming seriously impact code readability
Modules
M
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Variables
let data = ['First', 'Second', 'Third']; let total = data.length;
let that = this;
let e1, e2; e1 = document.getElementById('value1').innerHTML; e1 = document.getElementById('value2').innerHTML;
if (e1 > e2) {
// Do something }
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Functions
function showFailureTextDiv(flag) {
if (parseInt(flag) == 0) { document.getElementById('FailureTextDiv').style.display = "block"; }else { document.getElementById('FailureTextDiv').style.display = "none"; } return; }
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Classes
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Modules
import { utils } from 'utils/utils.js';
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Somewhere During Code Review
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Ethical JS Writing idiomatic JavaScript is the first step to write ethical code, on top of this it’s mandatory to apply best practices and master the platform
�ethical
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Topics
Review in practice how to master the execution context of JavaScript
Execution Context
M
Rethink how use a function, return always a value and minimize side effects
Functional
F
Evolve the code base to have a more manageable software
ESNext API
A Code readability starts with good names, and a clean syntax
Clean Syntax
D
A quick overview of a couple of libraries that can help improving your JavaScript
Libraries
L
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Mastering Execution Context
Never pass the context around by trapping it in variables that get enclosed in a closure, use the Function and Reflect API instead
Take Advantage of the Context
�
Be accurate when passing arguments to functions executed within a different context, avoid null values proliferating around the code base
Arguments �
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Execution Context
let func = () => { return arguments.length; } func.apply(void 0, null); // -> 0 Reflect.apply(func, void 0, null); // -> TypeError
let obj = document.createElement('object'); typeof obj; // -> "function", can be called
obj.apply; // -> undefined, no Function.prototype Reflect.apply(obj, thisArg, argList); // -> works properly
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Reflect vs Object
The Reflect module is a more natural place for many of the reflection methods previously defined on Object
Reflection
�
Many operations in Reflect are similar to ES5 operations defined on Object, such as Reflect.getOwnPropertyDescriptor and Reflect.defineProperty; anyway, the return value is usually more meaningful
Return Values �
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Clean Syntax
Never pass the context around by trapping it in variables that get enclosed in a closure, use the Function and Reflect API instead
Use the Context�
Be accurate when passing arguments to functions executed within a different context, avoid null values proliferating around the code base
Arguments �
The map(), filter(), and reduce() methods are a key element to get a cleaner syntax to filter data structures
Mapping and Filtering�
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Parens, Braces, Linebreaks
// Examples of really cramped syntax
if(condition) doSomething();
while(condition) iterating++;
for(var i=0;i<100;i++) someIterativeFn();
// Use whitespace to promote readability
if ( condition ) { // statements }
while ( condition ) { // statements }
for ( var i = 0; i < 100; i++ ) { // statements }
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Assignments, Declarations, Function
// Bad var foo = "", bar = ""; var qux;
function foo() { // some statements here var bar = "", qux; }
// Good var foo = ""; var bar = ""; var qux;
function foo() { var bar = "", qux; // all statements after the variables declarations. }
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Early Returns
function returnLate( foo ) { var ret;
if ( foo ) { ret = "foo"; } else { ret = "bar"; } return ret; }
function returnEarly( foo ) {
if ( foo ) { return "foo"; } return "bar"; }
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Mastering Coercions
// coercions
string === number; // -> false string === number + ""; // -> true +string === number; // -> true bool === number; // -> false +bool === number; // -> true bool === string; // -> false bool === !!string; // -> true
// evaluate truthiness
if ( array.length > 0 ) if ( array.length ) // -> Better
if ( array.length === 0 ) if ( !array.length ) // -> Better
if ( string !== "" ) if ( string ) // -> Better
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Be Functional
It’s not a buzzword, it’s a true different way to think about data structures and functions
Buzzword �
Functions are side effects free and always return a value
Functions�
Threat your model as a single source of truth
Immutability �
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Plato
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RxJS
RxJS is an implementation of the Observer pattern on steroids, it hides the complexity of loops and observing / subscribing
Hide Complexity�
It provides built in operators to debounce, take, throttle, etc. data streams
Built-in Operators�
By hiding the complexity, RxJS provide a pragmatic approach to declarative programming
Declarative Approach �
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Declarative Programming
const task_stream = // Makes a stream of all the tasks in the database getTasks(). // Get tasks only for this user filter((task) => task.user_id == user_id). // Get tasks that are uncompleted filter((task) => !task.completed). // Only get name of task map((task) => task.name)
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Conclusions
�ethical
Always write code as the maintainer is a psychopath that knows where you live
Try to oversimplify modules, and to keep the code simple
Never fight for a standard, fight only for maintainability and readability
Write easy to test code, when tests get complicated there are design flaws
When there’s no way to avoid complexity, hide it with an abstraction layer
http://www.jsfuck.com/
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Thanks!
�
Write Ethical JS
�
Modern API
�
Track the Tech Debt
�
Remove Unneeded Code
There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies, and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult..
-C.A.R. Hoare