How to use the Array.includes() function in ES6

This article mainly introduces the usage of the Array.includes() function in ES6. Friends who need it can refer to it. I hope it can help everyone.

In ES5, Array already provides indexOf to find the position of an element. If it does not exist, it returns -1. However, this function has two small parameters when determining whether the array contains an element. Disadvantages, the first is that it will return -1 and the position of the element to indicate whether it is included. There is no problem in terms of positioning, but it is not semantic enough. Another problem is that it cannot determine whether there are NaN elements.

const arr1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', NaN]
console.log('%s', arr1.indexOf(NaN))

Result:

-1

ES6 provides the Array.includes() function to determine whether a certain element is included, except that it cannot In addition to positioning, it solves the above two problems of indexOf. It directly returns true or false to indicate whether it contains an element, and it is also effective for NaN.

const arr1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', NaN]
console.log('%s', arr1.includes('c'))
console.log('%s', arr1.includes('z'))
console.log('%s', arr1.includes(NaN))

Result:

true
false
true

The second of the includes() function The parameter indicates the starting position of the judgment.

const arr1 = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', NaN]
console.log('%s', arr1.includes('d', 1))
console.log('%s', arr1.includes('d', 3))
console.log('%s', arr1.includes('d', 4))

Result:

true
true
false

The second parameter can also be a negative number, indicating from Count from the right, but do not change the direction of the search. The search direction is still from left to right.

console.log('%s', arr1.includes('k', -1))
console.log('%s', arr1.includes('k', -2))
console.log('%s', arr1.includes('i', -3))

Result:

false
true
false

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