“let” keyword:
This is basically a super local variable, it’s very useful for using them in for loops. Now you can have multiple nested for loops and declare all of your loop counter variables “i” and not worry about conflicts.
Example
Using var:
var i = 5;
for (var i = 0; i < 10; i++) {
// after last loop i equals 10
}
// Here i is 10
Using let:
let i = 5;
for (let i = 0; i < 10; i++) {
// after last loop i equals 10
}
// Here i is 5
“for of” statement
This is another way to loop through an array, I find it easier to write although it only works on iterables so this means it doesn’t work on objects as opposed to “for in” which works on both objects and arrays.
Example
Considering:
var array = [1];
Using “for in”:
for (let index in array){
let value = array[index];
//value equals 1
}
Using “for of”:
for (let value of array){
//value equals 1
}
String includes() Method
If you are like me and hate the sight of using .search() or regex to check if a string includes some text then you need this in your life.
Example
Considering the following string:
var myString = "Hello world";
Using search method:
var includesWorld = myString.search("world") != -1; //true
Using includes method:
var includesWorld = myString.includes("world"); //true
Array includes() Method
This is the same thing as the previous example with String includes() method. I find it easier and more elegant than using Array indexOf.
Example
Considering the following string:
var myArray = ["banana", "apple", "pear", "watermelon"];
Using indexOf method:
var includesWatermelon = myArray.indexOf("watermelon") != -1; //true
Using includes method:
var includesWatermelon = myArray.includes("watermelon"); //true
Array every() Method
This method is useful for validating if all of the elements of the array meet certain condition, if one of them doesn’t meet the condition then it returns false.
Example
var guestAges = [17,18,21,22,24];
var allAdults = guestAges.every( function (age){ return age >= 18; } );
//allAdults equals false because one of the guest ages is under 18
Set Object
The set object is a list of unique values of any type. This is very useful for removing duplicates from an Array.
Example
let myArray = [1,2,3,4,4,4,4,4,4,4,4,4,4,4,4,4,5];
let mySet = new Set(myArray); // mySet now equals {1, 2, 3, 4, 5}
let deDuplicatedArray = Array.from(mySet); //deDuplicatedArray now equals [1,2,3,4,5]
Here’s another example
let animals = new Set();
animals.add('pig');
animals.add('bear');
animals.add('cat');
animals.add('dog');
console.log(animals.size); // 4
animals.add('bear'); // Adding a duplicate
console.log(animals.size); // Still 4!
Spread syntax
This is basically used to expand an array or compact several parameters into an array.
Examples
Useful for concatenating two arrays like:
let array1 = ["bear", "wolf"]; let array2 = ["moose", ...array1 ]; //array2 equals ["bear","wolf","moose"]
Or making copies of arrays like:
let array1 = [1, 2, 3]; let array1Copy = array1; //This is a shallow copy let array1CopySpread = [...array1 ]; array1Copy.push(4); //Pushing to the shallow copy //array1 equals [1,2,3,4] //array1Copy equals [1,2,3,4] //array1CopySpread equals [1,2,3] //The copy using spread remains unmodified
Template literals (Template strings)
You can now use backtick characters (`) to have more freedom when defining strings, they also support placeholders and multi-line strings!
Example
Using string concatenation:
var myNumber = 23; var myString = 'text line 1\n' + 'text line 2\n' + 'text with "double quotes" and \'single quotes\'\n' + 'text with variable value of ' + myNumber;
Using template literals:
var myNumber = 23;
var myString =
`text line 1
text line 2
text with "double quotes" and 'single quotes'
text with variable value of ${myNumber}`;
The output is the same:
text line 1 text line 2 text with "double quotes" and 'single quotes' text with variable value of 23
Arrow functions
These functions work the same as regular functions but have a more compact syntax.
Example
Regular function:
function hello() {
return "Hello World!";
}
Arrow function:
hello = () => {
return "Hello World!";
}
And it can get even shorter:
hello = () => "Hello World!";
Anonymous arrow function with params:
((name)=> `Hello ${name}!`)('stranger'); //"Hello stranger!"
Server-side promises
Promises are now supported server-side so you can now write asynchronous code.
Example
https.get.promise({
url: 'https://jsonplaceholder.typicode.com/todos/1'
})
.then(function(response){
log.debug({
title: 'Response',
details: response
});
})
.catch(function onRejected(reason) {
log.debug({
title: 'Invalid Get Request: ',
details: reason
});
})
You can also create your own Promises now like so:
let promise = new Promise((resolve) => {
let response = https.get({url: 'https://jsonplaceholder.typicode.com/todos/1'});
resolve(response.body);
});
promise.then(log.debug); //This calls log.debug and uses whatever data is returned as parameter
Async functions (Async/Await)
Async functions provide a way to structure and simplify your asynchronous code. I find this very useful to avoid callback hell that comes with Promises as it can get pretty complex, I have seen some code where there’s an unending statements of .then.then.then….. in a row.
Example
async function asyncRequest(){ //<< Note the async keyword next to the function
let promise = new Promise((resolve) => {
let response = https.get({url: 'https://jsonplaceholder.typicode.com/todos/1'});
resolve(response.body);
});
//promise.then(log.debug); //No longer using this
let responseBody = await promise; //Using await instead
log.debug('responseBody', responseBody); //Logs correctly
}