Determine the length of the result from using the Array.prototype.some() method

Question

Determine the length of the result from using the Array.prototype.some() method

I have a conditional that is being checked using Array.prototype.some(). Take this array for example:

const coolArray = [
  { isCool: false },
  { isCool: false },
  { isCool: true }
]

const isCool = coolArray.some(item => item.isCool === true)

if (isCool) {
  console.log("Hello, I'm considered cool!")
}

But what if I want the check to only pass when item.isCool is true and at least two items in the array meet this condition? In such a case, the message would not be outputted as there's only one true condition.

The MDN documentation states that the syntax of this method is

arr.some(callback(element[, index[, array]])[, thisArg])

. However, the reference to [, array] in the callback function pertains to the original array instead of its clone. Therefore, modifying the code snippet like below yields the same result:

const isCool = coolArray.some((item, index, arr) => {
  return item.isCool === true && arr.length > 1
})

I understand that I could bypass using .some() and iterate over the array with map or for loops while storing results in an external array for later length comparison. A sample implementation is shown below:

const isCoolArr = []
coolArray.map(item => item.isCool ? isCoolArr.push(item) : false)
console.log('Expected outcome:', isCoolArr.length) // outputs 1

However, I am seeking simpler alternatives to achieve this. Is .some() suitable for my requirements, or should I consider other approaches apart from the ones mentioned earlier?

javascript arrays

Answer 1

Answer №1

Using Array.reduce

const awesomeArray = [
  { isAwesome: false },
  { isAwesome: true },
  { isAwesome: true }
]

const total = awesomeArray.reduce((sum, element) => Number(element.isAwesome) + sum, 0)

if (total >= 2) {
  console.log("Hey there, I'm awesome!")
}

Answer 2

Using Array.reduce

const awesomeArray = [
  { isAwesome: false },
  { isAwesome: true },
  { isAwesome: true }
]

const total = awesomeArray.reduce((sum, element) => Number(element.isAwesome) + sum, 0)

if (total >= 2) {
  console.log("Hey there, I'm awesome!")
}

Answer 3

Answer №2

When using .filter(), you do not have the advantage of short-circuiting that comes with .some(). One way to work around this is by utilizing a variable outside of the callback function.

const coolArray = [{isCool: false},{isCool: false},{isCool: true}]
let count = 0

const isCool = coolArray.some(item => (count += item.isCool) >= 2)

if (isCool) {
  console.log("hello I'm cool!")
} else {
  console.log("not cool enough")
}

This technique leverages the conversion of booleans into numbers. If you prefer a more explicit approach, there is an alternative available.

const coolArray = [{isCool: false},{isCool: false},{isCool: true}]
let count = 0

const isCool = coolArray.some(item => item.isCool && ++count >= 2)

if (isCool) {
  console.log("hello I'm cool!")
} else {
  console.log("not cool enough")
}

Another option is to achieve the same result without adding an extra variable.

const coolArray = [{isCool: false},{isCool: false},{isCool: true}]
let isCool = 0;

isCool = coolArray.some(item => item.isCool && ++isCool >= 2);

if (isCool) {
  console.log("hello I'm cool!")
} else {
  console.log("not cool enough")
}

Answer 4

When using .filter(), you do not have the advantage of short-circuiting that comes with .some(). One way to work around this is by utilizing a variable outside of the callback function.

const coolArray = [{isCool: false},{isCool: false},{isCool: true}]
let count = 0

const isCool = coolArray.some(item => (count += item.isCool) >= 2)

if (isCool) {
  console.log("hello I'm cool!")
} else {
  console.log("not cool enough")
}

This technique leverages the conversion of booleans into numbers. If you prefer a more explicit approach, there is an alternative available.

const coolArray = [{isCool: false},{isCool: false},{isCool: true}]
let count = 0

const isCool = coolArray.some(item => item.isCool && ++count >= 2)

if (isCool) {
  console.log("hello I'm cool!")
} else {
  console.log("not cool enough")
}

Another option is to achieve the same result without adding an extra variable.

const coolArray = [{isCool: false},{isCool: false},{isCool: true}]
let isCool = 0;

isCool = coolArray.some(item => item.isCool && ++isCool >= 2);

if (isCool) {
  console.log("hello I'm cool!")
} else {
  console.log("not cool enough")
}

Answer 5

Answer №3

One way to achieve this is by using the filter method and then checking the length of the resulting array

const coolArray = [
  { isCool: false },
  { isCool: false },
  { isCool: true }
]

const isCool = coolArray.filter(item => item.isCool === true)

if (isCool.length > 1 ) {
  console.log("hello I'm cool!")
} else{
  console.log('length is less than 2')
}

Answer 6

One way to achieve this is by using the filter method and then checking the length of the resulting array

const coolArray = [
  { isCool: false },
  { isCool: false },
  { isCool: true }
]

const isCool = coolArray.filter(item => item.isCool === true)

if (isCool.length > 1 ) {
  console.log("hello I'm cool!")
} else{
  console.log('length is less than 2')
}

Answer 7

Answer №4

Some individuals have recommended using the filter function and checking for the length. I propose creating a custom method called atLeast, which will stop once the condition is satisfied.

const amazingArray = [
  { isAmazing: false },
  { isAmazing: false },
  { isAmazing: true }
]

function checkCondition(cb, num) {
  let count = 0;
  for (let i = 0; i < this.length; i++) {
    if (cb(this[i], i, this)) count++;
    if (count === num) return true;
  }
  return false;
}

Object.defineProperty(Array.prototype, 'atLeast', {
  value: checkCondition,
  writeable: true
})

console.log(amazingArray.atLeast(x => x.isAmazing === true, 1)); //true
console.log(amazingArray.atLeast(x => x.isAmazing === true, 2)); //false

Answer 8

Some individuals have recommended using the filter function and checking for the length. I propose creating a custom method called atLeast, which will stop once the condition is satisfied.

const amazingArray = [
  { isAmazing: false },
  { isAmazing: false },
  { isAmazing: true }
]

function checkCondition(cb, num) {
  let count = 0;
  for (let i = 0; i < this.length; i++) {
    if (cb(this[i], i, this)) count++;
    if (count === num) return true;
  }
  return false;
}

Object.defineProperty(Array.prototype, 'atLeast', {
  value: checkCondition,
  writeable: true
})

console.log(amazingArray.atLeast(x => x.isAmazing === true, 1)); //true
console.log(amazingArray.atLeast(x => x.isAmazing === true, 2)); //false

Answer 9

Answer №5

Here is a basic implementation that terminates when the specified limit is reached:

let stopAtLimit = (array, fn, count) => array.some(x => !(count -= Boolean(fn(x))));

console.log(stopAtLimit(
    [1,2,3,44,5,66,7,99],
    x => x > 10,
    2
))

Alternatively,

let checkLimit = (fn, count) => x => !(count -= !!fn(x));
    

console.log(
    [1, 2, 3, 44, 5, 66, 7, 99].some(checkLimit(x => x > 10, 2))
)

In most scenarios, the premature exit optimization may not be necessary, and you can resort to using a more general counter function like this:

let countMatching = (array, fn) => array.reduce((n, x) => n + Boolean(fn(x)), 0);

console.log(countMatching(
    [1,2,3,44,5,66,7,99],
    x => x > 10
) >= 2)

Answer 10

Here is a basic implementation that terminates when the specified limit is reached:

let stopAtLimit = (array, fn, count) => array.some(x => !(count -= Boolean(fn(x))));

console.log(stopAtLimit(
    [1,2,3,44,5,66,7,99],
    x => x > 10,
    2
))

Alternatively,

let checkLimit = (fn, count) => x => !(count -= !!fn(x));
    

console.log(
    [1, 2, 3, 44, 5, 66, 7, 99].some(checkLimit(x => x > 10, 2))
)

In most scenarios, the premature exit optimization may not be necessary, and you can resort to using a more general counter function like this:

let countMatching = (array, fn) => array.reduce((n, x) => n + Boolean(fn(x)), 0);

console.log(countMatching(
    [1,2,3,44,5,66,7,99],
    x => x > 10
) >= 2)

Determine the length of the result from using the Array.prototype.some() method

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

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