Javascript Array find()

Introduction

The find() method returns the first element by the provided testing function. 

arr.find(callback(element[, index[, array]])[, thisArg])
Parameter
 Optional
 Meaning
callback




 Not




 Function to execute on each array element.
It takes 3 arguments:
element - current array element
index - Optional, the index of the current element.
array - Optional, the whole array.
thisArg
 Optional
 Object to use as this inside callback.

Find an object in an array by one of its properties 

const languages = [/*from  w  ww  . j av  a 2s.  c  om*/
  {name: 'HTML',  line: 2},
  {name: 'CSS',   line: 0},
  {name: 'Javascript', line: 5}
];

function isCSS(fruit) { 
  return fruit.name === 'CSS';
}

console.log(languages.find(isCSS)); 

//using arrow function
const result = languages.find( ({ name }) => name === 'CSS' );
console.log(result)

Find a prime number or return undefined if there is no prime number: 

function isPrime(element, index, array) {
  let start = 2;// www . j  a  va  2 s  .  c om
  while (start <= Math.sqrt(element)) {
    if (element % start++ < 1) {
      return false;
    }
  }
  return element > 1;
}

console.log([4, 6, 8, 12].find(isPrime)); // undefined, not found
console.log([4, 5, 8, 12].find(isPrime)); // 5

find() visits the nonexistent and deleted elements 

const array = [0,1,,,,5,6];/*from ww  w.  j av a2  s.c om*/
array.find(function(value, index) {
  console.log('Visited index ', index, ' with value ', value); 
});

array.find(function(value, index) {
  if (index === 0) {
    delete array[5];
  }
  // Element 5 is visited even though deleted
  console.log('Visited index ', index, ' with value ', value); 
});

More example 

const people = [{/*from  ww w  .  j av  a  2s. c  om*/
        name: "CSS",
        age: 27
    },
    {
        name: "HTML",
        age: 29
    }
];

console.log(people.find((element, index, array) => element.age < 28));
console.log(people.findIndex((element, index, array) => element.age < 28));

find() and findIndex() will continue searching once a match has been found. 

const evens = [2, 4, 6];/*w  w w . ja  v  a 2 s. co m*/

// Last element of array will never be inspected after match is found 
evens.find((element, index, array) => {
    console.log(element);
    console.log(index);
    console.log(array);
    return element === 4;
});



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