I am new to using recursion so I just want to know, if I want to know the index of an array element, by using recursion (Javascript). Is this the right way, or there is a better way?

let arr = [1, 2, 3, 4]

function search(arr, item) {
    const searchIndex = (array, elem, index = 0) => {
        if (array.length === 0) return -1
        if (array[0] === elem) return index
        return searchIndex(array.slice(1), elem,   index)
    }

    return searchIndex(arr, item)
}
console.log(search(arr, 4)) // output should be 3

CodePudding user response：

You could change the arguments a bit and add index and hand over the complete array.

function search(array, item, i = 0) {
    if (i >= array.length) return -1;
    if (array[i] === item) return i;
    return search(array, item, i   1);
}

let arr = [1, 2, 3, 4];
console.log(search(arr, 4)) // 3
console.log(search(arr, 8)) // -1
console.log(search([], 4)) // -1

An approach without an additional variable, but with slicing the array.

function search(array, item) {
    if (!array.length) return -1;
    if (array[0] === item) return 0;
    return search(array.slice(1), item)   1 || -1;
}

let arr = [1, 2, 3, 4, 5];
console.log(search(arr, 1)) // 0
console.log(search(arr, 2)) // 1
console.log(search(arr, 3)) // 2
console.log(search(arr, 4)) // 3
console.log(search(arr, 5)) // 4
console.log(search(arr, 8)) // -1
console.log(search([], 4)) // -1

.as-console-wrapper { max-height: 100% !important; top: 0; }

CodePudding user response：

Why not using Array.prototype.indexOf()?

Check more here

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

let arr = [1, 2, 3, 4]
console.log(arr.indexOf(4))

CodePudding user response：

const arr = ['1', '2', '3','4']
  
  const index = arr.indexOf('4');
  console.log(index)
  
  //index is `3`