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Sajith Pradeep
Sajith Pradeep

Posted on

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

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)
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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
})
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// 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
})
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Hope you guys learned something new today. Keep coding!!

Top comments (4)

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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";
});
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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.");
}
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Than this one.

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

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

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sajithpradeep profile image
Sajith Pradeep Author

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

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drfcozapata profile image
Francisco Zapata

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

This post blew up on DEV in 2020:

js visualized

πŸš€βš™οΈ JavaScript Visualized: the JavaScript Engine

As JavaScript devs, we usually don't have to deal with compilers ourselves. However, it's definitely good to know the basics of the JavaScript engine and see how it handles our human-friendly JS code, and turns it into something machines understand! πŸ₯³

Happy coding!