Javascript Arrays: find() vs Array findIndex and polyfills

Array methods to search for a particular element and its polyfills

Array.prototype.findIndex(predictFn):

1. it takes predict function as an argument and returns the index of the first element found and -1 if the element is not found.

let a = [1,2,3,"4",4]
a.findIndex((d) => d == 4) // returns 3
a.find((d) => d === "2") // returns -1

Array.prototype.find(predictFn)

1. it behaves exactly the same as above just that it returns the element’s value if found and undefined when it can’t find the element

let a = [1,2,3,"4",4]
a.find((d) => d == 4) // returns "4"
a.find((d) => d === "3") // returns undefined

polyfill for find

if you look closely at the above two functions they’re quite similar to Array.filter except

1. it returns just one value either index or an element and an empty array for the null case

Array.prototype.find = function(predictFn) {
     const arr = this; //captures the array
     const result = arr.filter(predictFn) //returning a first value 
     return result.length == 0 ? undefined : result[0]
}

above is a polyfill for find similar way you can write polyfill for findIndex too.

polyfill for findIndex

there are other functions available in the similar zone for eg indexOf and includes you can read about them here: https://hiraljs.medium.com/indexof-vs-includes-30ce7a356360

I find includes cleaner when it comes to usage and would not use other functions until I have very strong reasons to use them.