DEV Community

Sajith Pradeep
Sajith Pradeep

Posted on

Understanding the array methods Array.some() and Array.every() in JavaScript

#javascript #tutorial #webdev

There are lot of scenarios when we have an array of items and we need to check whether every item in that array satisfy a particular condition.

We might think that, why not use a for loop and flag to check this?

But there is an easier and much cleaner way to achieve this using Array.every().

Similarly, if we need to check if at least some items in an array satisfy a condition, we can use the Array.some() method.

Let us understand this better with some examples -

// We have a sample Array of persons from country ABC
const sampleArray = [
  {
    name: "John",
    occupation: "Doctor",
    age: 31,
    sex: "male",
    country: "ABC"
  },
  {
    name: "Jane",
    occupation: "Doctor",
    age: 26,
    sex: "female",
    country: "ABC"
  },
  {
    name: "Roger",
    occupation: "Engineer",
    age: 28,
    sex: "male",
    country: "ABC"
  },
  {
    name: "Riya",
    occupation: "Engineer",
    age: 32,
    sex: "female",
    country: "ABC"
  }
]

// I want to find out if all of them are from country "ABC"

const countryCheck = sampleArray.every(person => {
  return person.country === "ABC"
})
console.log("All are from the same country? ", countryCheck)

// I want to check if all are engineers
const engineerCheck = sampleArray.every(person => {
    return person.occupation === "Engineer"
})
console.log("All are Engineers? ", engineerCheck)

// I want to check if at least some women are engineers
const womenEngineers = sampleArray.some(person => {
    return person.occupation === "Engineer" && person.sex === "female"
})
console.log("Do we have at least some women engineers?", womenEngineers)

// I want to check if any of them are advocates
const lawyerCheck = sampleArray.some(person => {
return person.occupation === "Lawyer"
})
console.log("Do we have any lawyers?", lawyerCheck)
Enter fullscreen mode Exit fullscreen mode

Output
image

Syntax of Array.every() and Array.some() 

// Syntax
Array.every(callback)

const callback = (currentElement, index, array) => {
  // currentElement - current item in the array that we are iterating over over
  // index - index of the current item - optional
  // array - array that we are iterating over - optional
} 

// example usage
Array.every((currentElement) => {
    return currentElement > 1
})
Enter fullscreen mode Exit fullscreen mode 
// Syntax
Array.some(callback)

const callback = (currentElement, index, array) => {
  // currentElement - current item in the array that we are iterating over over
  // index - index of the current item - optional
  // array - array that we are iterating over - optional
} 

// example usage
Array.some((currentElement) => {
    return currentElement > 1
})
Enter fullscreen mode Exit fullscreen mode

Hope you guys learned something new today. Keep coding!!

Top comments (4)

Collapse
 
aminnairi profile image
Amin •

Since these methods return a boolean, I would suggest a better way of naming the variables that holds the return values of those methods so that we understand quickly what values these variables are holding and why they are being used in the source-code.

// It reads almost as plain english and this comment is useless
const someoneIsLawyer = persons.some(({occupation}) => {
  return occupation === "Lawyer";
});
Enter fullscreen mode Exit fullscreen mode

Because I have an easier time reading this code.

// Reads as plain english again
if (someoneIsLawyer) {
  console.log("Do something if there is a lawyer.");
}
Enter fullscreen mode Exit fullscreen mode

Than this one.

// What does it hold? A boolean? Is it a function?
if (lawyerCheck) {
  console.log("Do something if there is a lawyer.");
}
Enter fullscreen mode Exit fullscreen mode
Collapse
 
monfernape profile image
Usman Khalil •

Definitely makes sense. Boolean variables should has prefixes such as 'has, is' etc. in my opinion.

Collapse
 
sajithpradeep profile image
Sajith Pradeep •

Thanks for this comment. I will definitely incorporate this next time around. :)

Collapse
 
drfcozapata profile image
Francisco Zapata •

I'm clear now... Thanks!!!

Read next

kasir-barati profile image

Module declaration in TS

Mohammad Jawad (Kasir) Barati -

catundanatalia profile image

We are simplifying (literals(arrays and objects)) in Js.

Natália Catunda -

r0mymendez profile image

Deploying Docs-as-Code on AWS: Building Dynamic Documentation Sites in MkDocs and Docusaurus

Romina Mendez -

marcuskohlberg profile image

Building simple event-driven applications with Pub/Sub

Marcus Kohlberg -