What are the differences between JavaScript's Array.includes() and Array.indexOf()?
Alex K

JavaScript'sArray.includes() andArray.indexOf() are both array methods used to search for an element within an array, but they have some differences in functionality and usage. Here are the key differences between them: 1. Return value: -Array.includes() returns a boolean value (true orfalse) indicating whether the array includes the specified element. -Array.indexOf() returns the index of the first occurrence of the specified element in the array, or-1 if the element is not found. 2. Usage: -Array.includes() is primarily used to check if an array contains a specific element. It provides a simple and concise way to perform this check. -Array.indexOf() is more versatile and can be used to check if an element is present in an array and retrieve its index if it exists. 3. Strict equality comparison: -Array.includes() uses strict equality (===) to compare the elements. It checks for the presence of the specified element based on its value and type. -Array.indexOf() also uses strict equality (===) by default, but it allows you to provide a second parameter to specify a starting index for the search. 4. Support for NaN: -Array.includes() handles theNaN value correctly. It can detect the presence ofNaN in an array. -Array.indexOf() does not handleNaN correctly. It cannot reliably identify the index ofNaN within an array. 5. Return behavior: -Array.includes() immediately returnstrue as soon as it finds a match. It does not continue searching for additional occurrences. -Array.indexOf() returns the index of the first occurrence found. If you need to find all occurrences, you can use a loop or other techniques. Here are some examples that demonstrate the differences:

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const array = [1, 2, 3, NaN, 'hello'];

console.log(array.includes(2)); // Output: true
console.log(array.includes(4)); // Output: false
console.log(array.includes(NaN)); // Output: true

console.log(array.indexOf(2)); // Output: 1
console.log(array.indexOf(4)); // Output: -1
console.log(array.indexOf(NaN)); // Output: -1

In this example,array.includes(2) returnstrue because the element2 is present in the array.array.includes(4) returnsfalse since4 is not present.array.includes(NaN) returnstrue becauseNaN is considered to be present in the array. array.indexOf(2) returns1 as the index of the first occurrence of2.array.indexOf(4) returns-1 because4 is not found.array.indexOf(NaN) also returns-1 becauseindexOf() cannot correctly identify the index ofNaN. Choose the appropriate method based on your specific use case. If you only need to check if an element exists in an array,Array.includes() provides a simpler and more expressive syntax. If you require the index of the element or need to handle special cases likeNaN,Array.indexOf() is more suitable.

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