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A list of lesser know syntaxes and features of JavaScript
// void operator
void 0 // returns undefined
void (0) // returns undefined
void 'abc' // returns undefined
void {} // returns undefined
void (1 === 1) // returns undefined
void (1 !== 1) // returns undefined
void anyfunction() // returns undefined
// IIFE
(function () {
console.log('Normal IIFE called')
})()
// Normal IIFE called
void function () {
console.log('Cool IIFE called')
}()
// Cool IIFE called
// IIFE with a return
result = (function () {
// ... some code
return 'Victor Sully'
})()
// result: 'Victor Sully'
result = function () {
// ... some code
return 'Nathan Drake'
}()
// result: 'Nathan Drake'
// Constructor with brackets
const date = new Date()
const month = new Date().getMonth()
const myInstance = new MyClass()
// Constructor without brackets
const date = new Date
const month = (new Date).getMonth()
const myInstance = new MyClass
// with block example
const person = {
firstname: 'Nathan',
lastname: 'Drake',
age: 29
}
with (person) {
console.log(`${firstname} ${lastname} is ${age} years old`)
}
// Nathan Drake is 29 years old
// Tilde operator with indexOf
let username = "Nathan Drake"
if (~username.indexOf("Drake")) {
console.log('Access denied')
} else {
console.log('Access granted')
}
// custom functional properties
function greet () {
if (greet.locale === 'fr') {
console.log('Bonjour!')
} else if (greet.locale === 'es') {
console.log('Hola!')
} else {
console.log('Hello!')
}
}
greet()
// Hello!
greet.locale = 'fr'
greet()
// Bonjour!
// custom functional properties
function generateNumber () {
if (!generateNumber.counter) {
generateNumber.counter = 0
}
return ++generateNumber.counter
}
console.log(generateNumber())
// 1
console.log(generateNumber())
// 2
console.log('current counter value: ', generateNumber.counter)
// current counter value: 2
generateNumber.counter = 10
console.log('current counter value: ', generateNumber.counter)
// current counter value: 10
console.log(generateNumber())
// 11
// callee && caller
const myFunction = function () {
console.log('Current function: ', arguments.callee.name)
console.log('Invoked by function: ', arguments.callee.caller.name)
}
void function main () {
myFunction()
} ()
// Current function: myFunction
// Invoked by function: main
// Function constructor
const multiply = new Function('x', 'y', 'return x*y;');
multiply(2, 3)
// 6
//Normal template literal
`Hello ${username}!`
//Tagged template literal
myTag`Hello ${username}!`
// Defining a Tag for template literals
function highlight(strings, ...values) {
// here i is the iterator for the strings array
let result = ''
strings.forEach((str, i) => {
result += str
if (values[i]) {
result += `<mark>${values[i]}</mark>`
}
})
return result
}
const author = 'Henry Avery'
const statement = `I am a man of fortune & I must seek my fortune`
const quote = highlight`${author} once said, ${statement}`
// <mark>Henry Avery</mark> once said, <mark>I am a man of fortune
// & I must seek my fortune</mark>
// Getters & Setters
const user = {
firstName: 'Nathan',
lastName: 'Drake',
// fullname is a virtual field
get fullName() {
return this.firstName + ' ' + this.lastName
},
// validate age before saving
set age(value) {
if (isNaN(value)) throw Error('Age has to be a number')
this._age = Number(value)
},
get age() {
return this._age
}
}
console.log(user.fullName) // Nathan Drake
user.firstName = 'Francis'
console.log(user.fullName) // Francis Drake
user.age = '29'
console.log(user.age) // 29
// user.age = 'invalid text' // Error: Age has to be a number
// Plus operator
+'9.11' // returns 9.11
+'-4' // returns -4
+'0xFF' // returns 255
+true // returns 1
+'123e-5' // returns 0.00123
+false // returns 0
+null // returns 0
+'Infinity' // returns Infinity
+'1,234' // returns NaN
+dateObject // returns 1542975502981 (timestamp)
+momentObject // returns 1542975502981 (timestamp)
// Bang Bang operator
!!null // returns false
!!undefined // returns false
!!false // returns false
!!true // returns true
!!"" // returns false
!!"string" // returns true
!!0 // returns false
!!1 // returns true
!!{} // returns true
!![] // returns true
declarationBlock: {
// can be used to group logical code blocks together
var i, j
}
forLoop1: //The first for statement is labeled "forLoop1"
for (i = 0; i < 3; i++) {
forLoop2: //The second for statement is labeled "forLoop2"
for (j = 0; j < 3; j++) {
if (i === 1 && j === 1) {
continue forLoop1
}
console.log('i = ' + i + ', j = ' + j)
}
}
loopBlock4: {
console.log('I will print')
break loopBlock4
console.log('I will not print')
}
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