some, every, find, and findindex

Introduction

In this subunit, we'll explore some array methods with more specialized applications: some, every, find, and findindex. Unlike the methods in the last unit, you won't be using them all the time, but they are still essential for you to know. You will often use them in conjunction with the methods introduced in the last subunit. Again, these might not be the most conceptually intuitive methods, but stick with it, and you'll gain the tools you need to succeed in the professional world.

some/every

Goals

Understand what some and every do
Write your own version of some and every

some

Iterates through an array
Runs a callback on each value in the array
If the callback returns true for at least one single value, return true
Otherwise, return false
the result of the callback will always be a boolean

An Example

let numbers = [1, 2, 3];
numbers.some(function (value, index, array) {
  return value < 3;
});

// true

let numbers = [1, 2, 3];
numbers.some(function (value, index, array) {
  return value > 10;
});

// false

How Does It Work

function some(array, callback){
  for(let i = 0; i < array.length; i+ + ){
    if(callback(array[i], i, array) === true){
      return true;
    }
  }
return false;
}

Iterates through an array
Runs a callback on each value in the array
If the callback returns true for at least one single value, return true
Otherwise, return false

Using Some In A Function

function hasAdmin(arr) {
  return arr.some(function (value) {
    return value.admin;
  });
}

hasAdmin([
  { name: 'Colt', admin: true },
  { name: 'Poppy', admin: false },
]); // true

hasAdmin([
  { name: 'Colt', admin: false },
  { name: 'Poppy', admin: false },
]); // false

function hasQuestionMark(str) {
  return str.split('').some(function (value) {
    return value === ' ? ';
  });
}

hasQuestionMark('How are you feeling'); // false
hasQuestionMark('How are you feeling now?'); // true

When You Would Use Some

You need to determine if at least one value in an array exists, and you have to determine this by using a callback ( not includes/indexOf)
A simple alternative to using filter and seeing if the array contains at least one element

every

Iterates through an array
Runs a callback on each value in the array
If the callback returns false for any single value, return false
Otherwise, return true
the result of the callback will always be a boolean

An Example

let numbers = [1, 2, 3];
numbers.every(function (value, index, array) {
  return value > 0;
});

// true

let numbers = [1, 2, 3];
numbers.every(function (value, index, array) {
  return value > 2;
});

// false

How Does It Work

Iterates through an array
Runs a callback on each value in the array
If the callback returns false for any single value, return false
Otherwise, return true

function every(array, callback){
  for(let i = 0; i < array.length; i+ + ){
    if(callback(array[i], i, array) === false){
      return false;
    }
  }
  return true;
}

Using Every In A Function

function allVowels(str){
  return str.split('').every(function(value){
    return "aeiou".includes(value)
  });
}

allVowels('awesome 1); // false
allVowels('aiaieoeoiu');// true

function allIntegers(arr){
  return arr.every(Number.isInteger);
}

allIntegers([1,2,3,4,4,4,4]) // true
allIntegers([5,1,4,3,2.2]) // false

When You Would Use Every

You need to determine if every value in an array exists, and you have to determine this by using a callback
A simple alternative to using filter and seeing if the filtered array is of the same length as the original array

find/findIndex

Goals

Understand what find and findIndex do
Write your own version of find and findIndex

find

Iterates through an array
Runs a callback on each value in the array
If the callback returns true at any point, return the value in the array that we're iterating over
Otherwise, return undefined

An Example

let arr = [1, 2, 3];
arr.find(function (value, index, array) {
  return value === 2;
});

// 2

let arr = [1, 2, 3];
arr.find(function (value, index, array) {
  return value < 1;
});

// undefined

How Does It Work

Iterates through an array
Runs a callback on each value in the array
If the callback returns true at any point, return the value we're iterating over
Otherwise, return undefined

function find(array, callback) {
  for (let i = 0; i < array.length; i++) {
    if (callback(array[i], i, array) === true) {
      return array[i];
    }
  }
}

Using Find in a Function

function findOddNumber(arr) {
  return arr.find(function (value) {
    return value % 2 !== 0;
  });
}
findOddNumber([2, 3, 4, 5]); // 3
findOddNumber([4, 6, 8, 10]); // undefined

function ensureNoSubArrays(arr) {
  return arr.find(Array.isArray) === undefined;
}
ensureNoSubArrays([1, 2, [3, 4]]); // false
ensureNoSubArrays([1, 2, 3, 4]); // true

When You Would Use Find

You need to determine if a value in an array exists, and you have to determine this by using a callback
A simple alternative to using filter and accessing the first element of the filtered array

findIndex

Iterates through an array
Runs a callback on each value in the array
If the callback returns true for any single value, return the index at which that value is found
Otherwise, return -1

An Example

let arr = [1, 2, 3];

arr.findlndex(function (value, index, array) {
  return value < 2;
}); // 0

let arr = [1, 2, 3];

arr.findlndex(function (value, index, array) {
  return value > 3;
}); //-i

How Does It Work

Iterates through an array
Runs a callback on each value in the array
If the callback returns true for any single value, return the index at which that value is found
Otherwise, return -1

function findIndex(array, callback){
  for(let i = 0; i < array.length; i+ + ){
    if(callback(array[i], i , array) === true){
      return i;
    }
  }
return -1;
}

Using findIndex In A Function

function findPositionOfBoolean(list) {
  return list.findlndex(function (value, index, array) {
    return typeof value === 'boolean';
  });
}
findPositionOfBoolean([1, 3, false, true]); // 2
findPositionOfBoolean(['no booleans', 'around', 'these parts']); // -1

When You Would Use findindex

You need to determine the index of a value in an array if it exists, and you have to determine this by using a callback
A better version of indexOf to be used when a callback is necessary

Last modified: 10 March 2024