some() and every()

Introduction: some()

some() will check an array to see if at least one of its elements passes the given condition. If it does, it will break out of the some() method and return true. If nothing matches the condition, then it will return false.

some() is ideal for finding if an array contains a value. This is very similar functionality to the find() array method, however, the key difference is that some() will return a boolean whereas find() will either return the element if found or undefined.

Syntax

const values = [100, 200, 300, 400, 500];

const newArray = values.some((element, index, array) => {
  // Return true if it matches your condition. If it does, it will stop iterating and return true for the result of the array
  // Return false if the condition is not matched
});

Parameters

element: The current element in the array that we are working with

index: (Optional) The current index of where we are in the array

array: (Optional) The original array some was called on

Basic example

Let’s have a look at a couple of basic examples to help with the understanding of how some() will work.

Basic example 1: Condition matches

In this example, we have a matching condition. We check if the values are >= 3 and we have a 3 in the array. As soon as we meet this condition, which we do when we have the value of 3, you can see that the some() array method breaks out, stops looping, and returns a true value.

const values = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

const didMatchCondition = values.some((value, index) => {
  console.log({ index, value });
  if (value >= 3) {
    return true;
  }
});

console.log('didMatchCondition:', didMatchCondition);
// Return/output:
// index: 0 value: 0
// index: 1 value: 1
// index: 2 value: 2
// index: 3 value: 3
// didMatchCondition: true

Basic example 2: Condition doesn’t match

The code in this example is exactly the same as the last basic example. However, we now check if the values are >= 100, which none of them are.

You will see that all of the items are looped over, and the value returned from the some() array method is false.

const values = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

const didMatchCondition = values.some((value, index) => {
  console.log({ index, value });
  if (value >= 100) {
    return true;
  }
});

console.log('didMatchCondition:', didMatchCondition);
// Return/output:
// index: 0 value: 0
// index: 1 value: 1
// index: 2 value: 2
// index: 3 value: 3
// index: 4 value: 4
// index: 5 value: 5
// index: 6 value: 6
// index: 7 value: 7
// index: 8 value: 8
// index: 9 value: 9
// didMatchCondition: false

Practical examples

Let’s look at more practical applications of using the some() array method.

Practical example 1: Course Modules

In this example we have a list of modules as objects in an array. They each contain a name string and a isComplete boolean indicating if a module has been completed. We check each if each module has been completed with the some() array method which breaks out of the some() array method loop as soon as it finds a module that has been completed. When a module has been completed, true is returned and set as the value for isSomeCoursesFinished.

const modules = [
  { name: 'Introduction to Programming', isComplete: true },
  { name: 'HTML', isComplete: true },
  { name: 'CSS', isComplete: false },
  { name: 'JavaScript', isComplete: true },
];

const isSomeCoursesFinished = modules.some((currentModule, index) => {
  console.log('index', index);
  return currentModule.isComplete === true;
});

console.log(isCourseFinished);
// Returns:
// index 0
// true

Introduction: every()

every() will check if each of the values in an array matches the given condition. If all elements match the condition, it will return true. If it finds an element that does not match the condition, it will immediately break out of the every() array method and return false. In short, every() will check to ensure that every element in the array matches the given condition.

Syntax

const values = [100, 200, 300, 400, 500];

const newArray = values.every((element, index, array) => {
  // Return true if it matches your condition and every() will keep looping
  // Return false if the condition is not matched and it will immediately break out, and return false as the final result. This is because not "every" value is valid.
});

Parameters

element: The current element in the array that we are working with

index: (Optional) The current index of where we are in the array

array: (Optional) The original array every was called on

Basic examples

Let’s look at some basic examples of every() so we can see how it works.

Basic example 1: Conditions all met

In this example, we check that all of our values are greater than/equal (>=) to 0, which they all are. You will see that the every() has traversed through the entire array and then returned a value of true.

const values = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

const didAllMatchCondition = values.every((value, index) => {
  console.log('index:', index, 'value:', value);
  if (value >= 0) {
    return true;
  }
});

console.log('didAllMatchCondition:', didAllMatchCondition);
// index: 0 value: 0
// index: 1 value: 1
// index: 2 value: 2
// index: 3 value: 3
// index: 4 value: 4
// index: 5 value: 5
// index: 6 value: 6
// index: 7 value: 7
// index: 8 value: 8
// index: 9 value: 9
// didAllMatchCondition: true

Basic example 2: Conditions not met

In this example, we are checking if any values are equal to or below 3. Once we get to 4, this condition is no longer true so it breaks out of the loop and returns false.

const values = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];

const didAllMatchCondition = values.every((value, index) => {
  console.log('index:', index, 'value:', value);
  if (value <= 3) {
    return true;
  }
});

console.log('didAllMatchCondition:', didAllMatchCondition);
// index: 0 value: 0
// index: 1 value: 1
// index: 2 value: 2
// index: 3 value: 3
// index: 4 value: 4
// didAllMatchCondition: false

Practical examples

Let’s look at more practical applications of using the every() array method.

Practical example 1: Course modules

In this example we have a list of modules as objects in an array. They each contain a name string and a isComplete boolean indicating if a module has been completed. We check each if each module has been completed with the every() array method which breaks out of the every() array method loop as soon as it finds a module that hasn’t been completed. When a module has been completed, false is returned and set as the value for isCourseFinished.

const modules = [
  { name: 'Introduction to Programming', isComplete: true },
  { name: 'HTML', isComplete: true },
  { name: 'CSS', isComplete: false },
  { name: 'JavaScript', isComplete: true },
];

const isCourseFinished = modules.every((currentModule) => {
  return currentModule.isComplete === true;
});

console.log(isCourseFinished);
// Returns:
// false

Additional resources

MDN Web Docs: Array.prototype.some()

MDN Web docs: Array.prototype.every()

GeekforGeeks.com: What is the difference between every() and some() methods in JavaScript ?