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Array Analysis

Arrays have built-in methods to analyse the contents of the array. Most of these methods take a function that returns true or false as an argument. Such a function is called a predicate.

The built-in methods are meant to be used instead of a for loop or the built-in forEach method:

Example of analysis using a for loop :

const numbers = [1, 'two', 3, 'four'];
for (var i = 0; i < numbers.length; i++) {
  if (numbers[i] === 'two') {
    return i;
  }
}
// => 1

Example of analysis using a built-in method:

const numbers = [1, 'two', 3, 'four'];
numbers.indexOf('two');
// => 1

Some other helpful built-in methods that are available to analyze an array are shown below. See MDN for a full list of array methods.

From indexOf
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The indexOf() method returns the first index at which a given element can be found in the array, or −1-1 if it is not present.

const beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];

console.log(beasts.indexOf('bison'));
// expected output: 1

// start from index 2
console.log(beasts.indexOf('bison', 2));
// expected output: 4

console.log(beasts.indexOf('giraffe'));
// expected output: -1

References

From includes
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The includes() method determines whether an array includes a certain value among its entries, returning true or false as appropriate.

const numbers = [1, 'two', 3, 'four'];
numbers.includes(1);
// => true
numbers.includes('one');
// => false

References

From every
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The every() method tests whether all elements in the array pass the test implemented by the provided function. It returns a Boolean value. 2

const numbers = [1, 3, 5, 7, 9];
numbers.every((num) => num % 2 !== 0);
// => true

References

From some
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The some() method tests whether at least one element in the array passes the test implemented by the provided function. 3

const numbers = [1, 3, 5, 7, 9];
numbers.some((num) => num % 2 !== 0);
// => true

References

From find
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The find() method returns the value of the first element in the provided array that satisfies the provided testing function. If no values satisfy the testing function, undefined is returned. 4

const numbers = [1, 3, 5, 7, 9];
numbers.find((num) => num < 5);
// => 1

References

From findIndex
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The findIndex() method returns the index of the first element in the array that satisfies the provided testing function. Otherwise, it returns -1, indicating that no element passed the test. 5

const numbers = [1, 3, 5, 7, 9];
numbers.findIndex((num) => num > 7);
// => 4
numbers.findIndex((num) => num > 9);
// => -1

References

References