Defense Against The

JAVASCRIPT  Dark Arts

http://bit.ly/js-dark-arts

James Q Quick

DEVELOPER. SPEAKER. TEACHER.

@jamesqquick

www.learnbuildteach.com

STICKERS!!!

Tweet me @jamesqquick and include hashtag #LearnBuildTeach

Why This Talk??

JavaScript is SCARY!!

On to the spells...

Mastering Equality

1.

"Dobby is a free elf!"

Double Equals

//Double equals compares loose equality using coercion
1 == '1' //true
false == 0 //true
false == '0' //true
0 == "" // true
"" == false //true
null == undefined //true

"Falsy Values"

//false
//0
//"",
//null
//undefined
//NAN

"Falsy Values"

function printName(name){
    if(!name){
        console.log("YOU AINT GOT NO NAME!!");
    }
    else {
        console.log(name);
    }
}

printName() //YOU AINT GOT NO NAME!!
printName("James") //James

Triple Equals

//Triple equals compares strong equality
//by comparing both type and value without coercion

1 === 1 //true
'Dark Arts' === 'Dark Arts' //true
true === true
1 === '1' //false
false === 0 //false
false === '0' //false
0 === "" // false
"" === false //false

Pass by Value

//Primitives are passed by value
//Primitives - undefined, null, boolean, string, number
let name = "James Quick";
const name2 = name;

console.log(name == name2); //true
console.log(name === name2); //true

name = "Jessica Quick";
console.log(name == name2); //false
console.log(name === name2); //false

Pass by Value (cont.)

name =

"James Quick"

name2 =

"James Quick"

let name = "James Quick";
const name2 = name;

console.log(name == name2); //true
console.log(name === name2); //true

name = "Jessica Quick";
console.log(name == name2); //false
console.log(name === name2); //false

Pass by Value (cont.)

name =

"Jessica Quick"

name2 =

"James Quick"

let name = "James Quick";
const name2 = name;

console.log(name == name2); //true
console.log(name === name2); //true

name = "Jessica Quick";
console.log(name == name2); //false
console.log(name === name2); //false

Pass By Reference

//Objects are passed by reference
const p1 = {
    first: 'James',
    last: 'Quick',
}

let p2 = p1;
console.log(p2 === p1); //true

p1.first = "Jessica";
console.log(p2.first) //"Jessica"

p2 = { ...p1 };
console.log(p2 === p1); //false

Pass by Reference (cont.)

p1 =

p2 =

{

    first: 'James',

    last: 'Quick'

}

const p1 = {
    first: 'James',
    last: 'Quick',
}

let p2 = p1;
console.log(p2 === p1); //true

p1.first = "Jessica";
console.log(p2.first) //"Jessica"

p2 = { ...p1 };
console.log(p2 === p1); //false

Pass by Reference (cont.)

p1 =

p2 =

{

    first: 'Jessica',

    last: 'Quick'

}

const p1 = {
    first: 'James',
    last: 'Quick',
}

let p2 = p1;
console.log(p2 === p1); //true

p1.first = "Jessica";
console.log(p2.first) //"Jessica"

p2 = { ...p1 };
console.log(p2 === p1); //false

Pass by Reference (cont.)

p1 =

{

    first: 'Jessica',

    last: 'Quick'

}

const p1 = {
    first: 'James',
    last: 'Quick',
}

let p2 = p1;
console.log(p2 === p1); //true

p1.first = "Jessica";
console.log(p2.first) //"Jessica"

p2 = { ...p1 };
console.log(p2 === p1); //false

p2 =

{

    first: 'Jessica',

    last: 'Quick'

}

Use triple equals and make true copies of objects to avoid confusion.

ES6 Features

2.

YOU MUST KNOW ES6!!

Default Parameters

const add = (num1, num2) => {
    return num1 + num2;
}

console.log(add()) //NaN

Default Parameters ES5

const add = (num1, num2) => {
    if (num1 === undefined) {
        num1 = 0;
    }
    if (num2 === undefined) {
        num2 = 0;
    }
    return num1 + num2;
}
console.log(add()); //0

Default Parameters ES5

const add = (num1, num2) => {
    num1 = num1 || 0;
    num2 = num2 || 0;
    return num1 + num2;
}
console.log(add());

Default Parameters ES6

const add = (num1 = 0, num2 = 0) => {
    return num1 + num2;
}
console.log(add()); //0

Default Parameters ES5 Again

const addFromObject = (obj) => {
    return obj.num1 + obj.num2; 
    //cannot read property of undefined
}

console.log(addFromObject());

Default Parameters ES6 Again

const addFromObject = ({ num1 = 0, num2 = 0 } = {}) => {
    return num1 + num2;
}

console.log(addFromObject()); //0

Default Parameters Error Function


function requiredArg() {
    throw new Error('The argument is required');
}
function add(x = requiredArg(), y = requiredArg()) {
    return x + y;
}

add()//Error THE ARGUMENT IS EQUIRED

Template Literal Strings

let markup = "<html>\n\t<head>\n\t</head>\n\t<body>\n\t</body>\n</html>"

markup = "<html>\n\t<head>\n\t" +
    "</head>\n\t<body>\n\t</body>\n</html>"

markup = 
`<html>
    <head>
    </head>
    <body>
    </body>
<html>`;

Template Literal Strings

const printPerson = (person) => {
    console.log(person.first + " " + person.last + " lives in " + person.city + "." );
    
    console.log(`${person.first} ${person.last} lives in ${person.city}.`);
}
printPerson({first: "James", last: "Quick", city: "Memphis"});

Spread Operator - Arrays

//Make shallow copies of arrays with the spread operator

const arr1 = [1, 2, 3, 4];
const arr2 = arr1;

arr1[0] = 15;
console.log(arr2[0]); //15

console.log(arr1 == arr2); //true

const arr3 = [...arr1];
console.log(arr3 == arr1); //false

Spread Operator - Objects

//Make shallow copies of objects with the spread operator

const p1 = {
    first: 'James',
    last: 'Quick',
};

let p2 = p1;
console.log(p2 === p1); //true

p2 = { ...p1 };
console.log(p2 === p1); //false

Deep Copy? Use lodash

OR...

JSON.parse(JSON.stringify(obj))

Other ES6 Features

  • Arrow Functions
  • Promises
  • Enhanced Object Literals
  • Rest Operator
  • Const and Let variables

YOU MUST KNOW ES6!!

JavaScript 30 by Wes Bos

Asynchronous JavaScript

3.

JavaScript is SINGLE THREADED

What the Heck is the Event Loop Anyway?!

Callbacks

//Run code after a delay
setTimeout(() => {
    console.log("1 second");
}, 1000);

//Add click event handler for a button
button.addEventListener('click', (e) => {
    console.log("Button was clicked");
});

Callback Hell

setTimeout(() => {
    console.log("5");
    setTimeout(() => {
        console.log("4");
        setTimeout(() => {
            console.log("3");
            setTimeout(() => {
                console.log("2");
                setTimeout(() => {
                    console.log("1");
                }, 1000)
            }, 1000)
        }, 1000)
    }, 1000)
}, 1000)

//5...4...3...2..1

Promises

const axios = require('axios');

const url = "http://api.icndb.com/jokes/random?firstName=James&lastName=Quick"
axios.get(url)
    .then( res => {
        console.log(res.data.value.joke);
        //"Product Owners never ask James Quick for more features. They ask for mercy."
    })
    .catch( err => {
        console.log(err);
    });

What if you need to run multiple async actions in a row?

Promise Chaining

const todoURL = "https://jsonplaceholder.typicode.com/todos/1";
const userURL = "https://jsonplaceholder.typicode.com/users/"

axios.get(todoURL)
    .then((res) => {
        console.log(res.data); //userId = 1
        return axios.get(userURL + res.data.userId);
    })
    .then(res => {
        console.log(res.data) //user object
    })
    .catch(err => {
        console.log("ERROR! " + err);
    })

Async/Await

const getJokeAsync = async () => {
    const url = "http://api.icndb.com/jokes/random?firstName=James&lastName=Quick"
    const res = await axios.get(url);
    console.log(res.data.value.joke);
}

getJokeAsync();

Async/Await

const getUserFromTodoAsync = async (todoId) => {
    const todoURL = "https://jsonplaceholder.typicode.com/todos/" + todoId;
    const userURL = "https://jsonplaceholder.typicode.com/users/"

    const res = await axios.get(todoUrl);
    const userRes = await axios.get(userURL + res.data.userId);
}

Async/Await and Try/Catch

const getTodoAsync = async () => {
    const todoURL = "https://jsonplaceholder.typicode.com/todos/1";
    const userURL = "https://jsonplaceholder.typicode.com/users/"

    try {
        const res = await axios.get(todoUrl);
        const userRes = await axios.get(userURL + res.data.userId);
    } catch (ex) {
        console.log("ERROR!" + ex);
    }
}

getTodoAsync();

Formatting and Linting

4.

What is LINTING?

Linting Benefits

  • Consistent Code Formatting
  • NO const reassignment and no undeclared variables
  • Better timing/performance with Asynchronous JS
  • No console.log()

Formatting Before and After

const name = "James";

const person = { first: name,last:"Quick"}

function printPersonName(p){
console.log(p.first, p.last);
}

...

const name = 'James';

const person = { first: name, last: 'Quick' };

function printPersonName(p) {
  console.log(p.first, p.last);
}

No Const Reassignment

No Undeclared References

Better Async Performance

No Console Log

Write BETTER code FASTER

Linting Setup

  • Install eslint package to project
  • Use `eslint --init` command 
  • follow prompts to create eslint configuration (creates .eslintrc file)
  • Install eslint extension for VS Code
  • Go into settings and check "Eslint: Auto Fix on Save"

Linting JavaScript

npm init
npm install --save eslint
eslint --init

ESLint Configuration File

{
    "env": {
        "browser": true,
        "commonjs": true,
        "es6": true
    },
    "extends": "eslint:recommended",
    "globals": {
        "Atomics": "readonly",
        "SharedArrayBuffer": "readonly"
    },
    "parserOptions": {
        "ecmaVersion": 2018
    },
    "rules": {
        "indent": [
            "error",
            "tab"
        ],
        "linebreak-style": [
            "error",
            "unix"
        ],
        "quotes": [
            "error",
            "single"
        ],
        "semi": [
            "error",
            "always"
        ]
    }
}

Preconfigured with the top front-end frameworks

TypeScript

5.

TypeScript is a typed superset of JavaScript that compiles to plain JavaScript. 

The benefits...

 Benefits of TypeScript

  • Optional static typings
  • Converts to JavaScript
  • Easily define object definitions with Interfaces
  • Documentation and Intellisense

Static Bindings - 1

function ICanAdd( num1, num2) {
    return num1 + num2;
}

ICanAdd(1,2);
ICanAdd("James", "Quick");
ICanAdd({}, []);

Static Bindings - 2

function ICanAdd(num1: number, num2: number) {
    return num1 + num2;
}

ICanAdd(1, 2);
ICanAdd("James", "Quick"); //CANT DO THAT!
ICanAdd({}, []); //CANT DO THAT!

Static Bindings - 3

function ICanAdd(num1: number, num2: number):number {
    return num1 + num2;
}

const num:number = ICanAdd(1, 2);

Static Bindings - 4


function ICanAdd(num1: number, num2: number):number {
    return num1 + num2;
}

const num = ICanAdd(1, 2); //type of number is optional since function returns a number

Static Bindings - 5


function ICanAdd(num1: number, num2: number):number {
    return num1 + num2;
}

const num = ICanAdd(1, 2);
num = "James" //YOU CAN"T DO THIS: num is of type number

Compilation -Before/After

const message: string = 'hello world';

const first = 'James';

const person = { first, last: 'Quick', age: 28 };

const { last, age } = person;

console.log(`${first} ${last} is ${age} years old!`);
var message = 'hello world';
var first = 'James';
var person = { first: first, last: 'Quick', age: 28 };
var last = person.last, age = person.age;
console.log(first + " " + last + " is " + age + " years old!");

Try out the TypeScript Playground

Interfaces/Models

interface Person  {
    first: string,
    last: string,
    age:number,
    children: [],
    spouse:Person
}

Documentation

Setup TypeScript

  • Install TypeScript via NPMx
  • Use tsc command followed by TypeScript file
  • Create TypeScript configuration file
  • Install TSLint extension VS Code

TypeScript Config

{
  "compilerOptions": {
    /* Basic Options */
    // "incremental": true,                   /* Enable incremental compilation */
    "target": "es5",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
    // "lib": [],                             /* Specify library files to be included in the compilation. */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    // "outDir": "./",                        /* Redirect output structure to the directory. */
    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "composite": true,                     /* Enable project compilation */
    // "tsBuildInfoFile": "./",               /* Specify file to store incremental compilation information */
    // "removeComments": true,                /* Do not emit comments to output. */
    // "noEmit": true,                        /* Do not emit outputs. */
    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */

    /* Strict Type-Checking Options */
    "strict": true,                           /* Enable all strict type-checking options. */
    // "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
    // "strictNullChecks": true,              /* Enable strict null checks. */
    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
    // "strictBindCallApply": true,           /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */

    /* Additional Checks */
    // "noUnusedLocals": true,                /* Report errors on unused locals. */
    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */

    /* Module Resolution Options */
    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                       /* List of folders to include type definitions from. */
    // "types": [],                           /* Type declaration files to be included in compilation. */
    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    "esModuleInterop": true                   /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */
    // "allowUmdGlobalAccess": true,          /* Allow accessing UMD globals from modules. */

    /* Source Map Options */
    // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */

    /* Experimental Options */
    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
  }
}

Configurable with the top front-end frameworks

Debugging

BONUS:

console.log()

Visual Studio Code

Learn VS Code

Coupon Code - KCDC2019

Wrap Up and Resources

Useful Links

www.learnbuildteach.com

STICKERS!!!

Tweet me @jamesqquick and include hashtag #LearnBuildTeach

THANK YOU!

@jamesqquick