An introduction to the small features that both ES7 & ES8 brings. If contributing please read the contributions section and check back from time to time for intermittent updates.
Object.entries
gives us the ability to get an object's enurmerable property pairs by returning an array of any given
object's own eumberable properties. /ie: [key, value] pairs. Note that the order is the same as provided by the for...in
loop.
Object.entries(obj)
- @params:
obj
- returns: Array
basic example
const obj = { self: 'that', norf: 'quux' }
console.log(Object.entries(obj))
// => [ ['self', 'that'], ['norf', 'quux'] ]
array like object with random key ordering
const obj = { 50: 'a', 1: 'b', 5: 'c' }
console.log(Object.entries(obj))
// => [ ['1', 'b'], ['5', 'c'], ['50', 'a'] ]
Object.values
lets us return an array of a given object's own enumerable property values. Note that the order is the
same as provided by the for...in
loop.
Object.values(obj)
- @params:
obj
- returns: Array
basic example
const obj = { a: 100, b: 200 }
console.log(Object.values(obj))
// => [100, 200]
mixed
const obj = { foo: 'foo', bar: [100, 200], baz: 55 }
console.log(Object.values(obj))
// => ['foo', [100, 200], 55 ]
string
const myStr = 'Lufthansa'
console.log(Object.values(myStr))
// => ["L", "u", "f", "t", "h", "a", "n", "s", "a"]
This one is a bit like indexOf
and very useful to the language by relying on returinng true or false, not 0
.
arr.inlcudes(searchEl[, fromIndex])
- @searchElement: the element to search for
- @fromIndex: pos in array at which to begin searching
- returns: Boolean
basic examples
[1, 2, 3].includes(-1) // false
[1, 2, 3].includes(1) // true
[1, 2, 3].includes(3, 4) // false
[1, 2, 3].includes(3, 3) // false
[1, 2, NaN].includes(NaN) // true
['foo', 'bar', 'quux'].includes('foo') // true
['foo', 'bar', 'quux'].includes('norf') // false
if
fromIndex
is greater than or equal to the len of array, false is automatically returned
let arr = ['x', 'y', 'z'];
arr.includes('x', 3) // false
arr.includes('z', 100) // false
This method, padStart()
pads the current string (applied from the left) with another string till the
resulting string reaches the given optional length.
str.padStart(targetLength [, padString])
- @targetLength: the length of resulting string once padding occurs
- @padString(Optional): the string to pad the current string with
- returns: String
basic examples
'xyz'.padStart(5) // " xyz"
'xyz'.padStart(10) // " xyz"
'xyz'.padStart(6, 'hij') // "hijxyz"
'xyz'.padStart(8, '1') // "11111xyz"
const myStr = 'xyz'.padStart(22) // " xyz"
myStr.length // 22
This method, padEnd()
pads the current string (applied from the right) with another string till the
resulting string reaches the given optional length.
str.padEnd(targetLength [, padString])
- @targetLength: the length of resulting string once padding occurs
- @padString(Optional): the string to pad the current string with
- returns: String
basic examples
'abc'.padEnd(10) // "abc "
'abc'.padEnd(10, "foo") // "abcfoofoof"
'abc'.padEnd(6, "123456") // "abc123"
'abc'.padEnd(1) // "abc"
A shorthand method to exponetiation has been introduced in JavaScript:
operand
**operand
basic examples
Math.pow(5, 2)
// ...is now
5 ** 2
Trailing commas are now allowed in JavaScript - they are now ignored
trailing commas in array
let arr = [
10,
20,
30,
40,
50,
]
arr // [10, 20, 30, 40, 50]
arr.length // 5
trailing commas in object
const obj = {
trailing: 'comma',
is: 'allowed',
in: 'JavaScript..',
}
Object.getOwnPropertyDescriptors()
returns all own property descriptors of a given object. A property descriptor
is a record with one of the following attributes:
- value
- writable
- get
- set
- configurable
- enumerable
let myObj = {
property1: 'foo',
property2: 'bar',
property3: 42,
property4: () => console.log('prop4')
}
Object.getOwnPropertyDescriptors(myObj)
/*
{ property1: {…}, property2: {…}, property3: {…}, property4: {…} }
property1: {value: "foo", writable: true, enumerable: true, configurable: true}
property2: {value: "bar", writable: true, enumerable: true, configurable: true}
property3: {value: 42, writable: true, enumerable: true, configurable: true}
property4: {value: ƒ, writable: true, enumerable: true, configurable: true}
__proto__: Object
*/
The asynchronous function returns an AsyncFunction
object and operates asynchronously via the event loop. The syntax is
very similar to synchronous functions
- async function name([param[, param[, ... param]]]) { statements }
- @name: the function name
- @param: param of the function
- statements: body of the function
- returns: Promise
const resolveAfter3Seconds = function() {
console.log('starting 3 second promsise')
return new Promise(resolve => {
setTimeout(function() {
resolve(3)
console.log('done in 3 seconds')
}, 3000)
})
}
const resolveAfter1Second = function() {
console.log('starting 1 second promise')
return new Promise(resolve => {
setTimeout(function() {
resolve(1)
console.log('done, in 1 second')
}, 1000)
})
}
const sequentialStart = async function() {
console.log('***SEQUENTIAL START***')
const one = await resolveAfter1Second()
const three = await resolveAfter3Seconds()
console.log(one)
console.log(three)
}
sequentialStart() // invoke async function
Contributions in the form of code samples and syntax are welcome - if you spot errors in example code or feel you have a better use case for a given feature please issue a pull request. Typos and formatting requests are also considered.