Russian roulette
JavaScript
Read fire tipCounting all array elements that match a condition
JavaScript
Want to know how many elements in an array match a condition? We can use this to count all elements in an array that return true for a function that checks this condition.
// takes an array and a function to check each element in the array against
const countBy = (array, checkFunction) => {
return array.reduce((count, element) => {
return checkFunction(element) ? count + 1 : count
}, 0)
}
// we can count how many numbers in an array are smaller than a given limit
countBy([-4, 3, -7, 5, 0, -3, 1, -8], number => number < 0)
// ⇒ 4
// we can count how many strings are exactly four characters long
countBy(['John', 'Paul', 'George', 'Ringo'], name => name.length === 4)
// ⇒ 2
// we can also check if objects have a certain value in a property
countBy([
{
name: 'Bulbasaur',
types: ['Grass', 'Poison']
}, {
name: 'Nidoqueen',
types: ['Poison', 'Ground']
}, {
name: 'Abra',
types: ['Psychic']
}, {
name: 'Tentacool',
types: ['Water', 'Poison']
}
], pokemon => pokemon.types.includes('Poison'))
// ⇒ 3