JS: ES6 Tips and Tricks
Enforcing Required Parameter
Throw an error if the function is called without parameter
let required = () => {
throw new Error('Missing parameters');
}
let add = (a: required(), b: required()) => {
return a + b;
}
console.log(add(1, 2)) // => 3
console.log(add(1)) // => error! missing parameters
Using Reduce to map and filter simultaneously
The benefit of using reduce comes into play when you want to ‘map’ and ‘filter’ together and you have a lot of data to go over.
If you’re chaining the ‘map’ and ‘filter’together you’re doing the work twice.
let numbers = [10, 20, 30, 40];
let doubledOver50 = numbers.reduce((finaList, number) => {
// double each number (i.e: map method)
number = number * 2;
// filter
if (number > 50)
finalList.push(number);
return finalList;
}, [] as number[]);
console.log(doubledOver50); // => [60, 80]
Counting Duplicate Array Items
let fruits = ['banana', 'cherry', 'orange', 'apple', 'cherry', 'orange', 'apple', 'banana', 'cherry', 'orange', 'fig'];
let count = fruits.reduce((tally, fruit) => {
tally[fruit] = (tally[fruit] || 0) + 1;
return tally;
}, {});
console.log(count); // => { banana: 2, cherry: 3, orange: 3, apple: 2, fig: 1 }
Object Destructuring for Array Item
const csvFile = "2018,John Smith,US,john@email.com,Washington";
const { 0: year, 1: fullName, 2: country, 3: email, 4: state } = csvFile.split(",");
console.log(`state: ${state} - country: ${country}`); // => state: Washington - country: US
Clearing or Truncating an Array
// truncating an array
const numbers = [11, 22, 33, 44, 55];
numbers.length = 2;
console.log(numbers); // => [11, 22]
// clearing an array
numbers.length = 0;
console.log(numbers); // => []
console.log(numbers[2]); // => undefined
// similar to "number = []". This will create a grabage but in JS grabage collector is not expensive
number = [];
Formatting JSON Code
const obj = {
foo: { bar: [11, 22, 33, 44], baz: { bing: true, boom: 'Hello' } }
};
JSON.stringify(obj, null, 4); // => formatted with indentiation
Remove Duplicate Items From an Array
const removeDupItems = arr => [...new Set(arr)];
removeDupItems([20, 'bar', 20, 'bar', true, true]); // => [20, 'bar', true]