const arr = [1, 2, '2', 3, 3, 4, 4, 5];
const result = [...new Set(arr)];
console.log(result);output:
[ 1, 2, '2', 3, 4, 5 ]arr using a Set, which only allows unique values.new Set(arr): Creates a new Set from the array. The Set will only keep unique values.[...new Set(arr)]: The spread operator ... is used to convert the Set back into an array.The output of console.log(’10’ – 5) is 5.
To find how many elements of an array fall between two values ‘a’ and ‘b’, we can use the ‘filter’ method. This method allows us to iterate over the array and apply a condition to each element, returning a new array with the elements that meet the condition. We can get the count of elements by using the length.
const array = [5, 10, 15, 20, 25, 30];
const a = 10;
const b = 25;
const newArray = array.filter(element => element >= a && element <= b);
const count = newArray.length;
console.log(newArray); // Output: [10, 15, 20, 25];
console.log(count); // Output: 4If we want to add a constant value to each element in an array(assuming the array contains numbers), we can use the ‘map’ method.
const array = [1, 2, 3, 4];
const constantValue = 7;
const newArray = array.map(element => element + constantValue);
console.log(newArray); // Output: [8, 9, 10, 11]To set the focus on an element with a specific ‘data-testid’ , we can use the ‘useEffect’ hook to find the element and then call its ‘focus’ method.
import React, { useEffect } from 'react';
const MainMenu = () => {
useEffect(() => {
// Locate the required element with data-testid
const mainMenuElement = document.querySelector('[data-testid="main-menu"]');
if(mainMenuElement && mainMenuElement instanceof HTMLElement) {
mainMenuElement.focus();
}
}, []);
return(
<div
data-testid="main-menu"
tabIndex="0" // Ensure the element can receive focus.
>
Main Menu content
<div>Other Content</div>
</div>
);
}
export default MainMenu;