We gonna use ECMAScript 2016’s new includes() method to determine whether an array contains a specific element. The new method includes(searchElement, fromIndex) function searches an array for a specific value and returns the corresponding boolean, return true if it exists otherwise false. An optional argument fromIndex allows to search from a specific index.
Let’s see some basic examples:
var a = [1, 2, 3]; a.includes(2); // true a.includes(4); // false
Syntax of includes()
arr.includes(searchElement) arr.includes(searchElement, fromIndex)
Parameters
searchElement – The element to search for.
fromIndex(Optional) – Default value is zero. The position in this array at which to begin searching for searchElement. A negative value searches from the index of array.length + fromIndex by asc.
Let’s see concise examples:
let technologies = ['PHP', 'JS', 'Ruby','NodeJS'];
technologies.includes('PHP', 1); // => false
technologies.includes('JS', 1); // => true
technologies.includes('Ruby', 10); // => false
technologies.includes('PHP', -3); // => false
technologies.includes('NodeJS', -3); // => true
'PHP' element has index 0 in technologies. However the search starts from 1 and the index 0 is skipped, so the element is not found.
'JS' has index 1, thus the search starts from index 1 , so include() is able to find it.
The 'Ruby' element is checked from index 10, which is bigger than the array length 4. includes() method for such situations returns false.
The index to begin searching parameter is a negative number -3 and the search starts from index 4 - 3 = 1. The searched 'PHP' is compared only with 'JS', 'Ruby' and 'NodeJS' elements, so there is no match.
When searching for 'NodeJS' element with the same -3 offset, it is a matches.
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