JavaScript recursion used to generate arrays, according to the teachings of Codecademy

Question

JavaScript recursion used to generate arrays, according to the teachings of Codecademy

      Looking to create a recursive function that calculates the powers of a number and adds each result to an array named "stack".

This means that with each recursion, a new value will be appended to the stack.

For instance, if we use power(3, 3), our stack should then contain: [3, 9, 27].

The issue I'm encountering is getting only the last power value (27) instead of the full array. What could be wrong in my code?

// Initialize an empty array called "stack"
var stack = [];
// Recursive function implementation
function power(base, exponent) {
    // Base case 
    if (exponent === 0) {
        return 1;
    }
    // Recursion case
    else {
        stack[exponent - 1] = base * power(base, exponent - 1);
        return stack[exponent - 1];
    }
}
power(3, 3);

javascript arrays recursion

Answer 1

Answer №1

Everything seems fine in your code except for the return value. Here is a slightly minified version of your code:

var task = (() => {
  var stack = [];
  function power(base, exponent) {
    return (exponent && (stack[--exponent] = base * power(base, exponent))) || 1;
  }
  power(3, 3);
  return stack;
});
console.log(task());

I personally don't prefer using recursive calls unless absolutely necessary.

In this scenario (assuming it's not just an exercise), there are alternative ways to achieve the same result. For example, using a classic for loop:

function power(base, exp){
  var result = [];
  for(var i=1; i<=exp; i++){
    result.push(Math.pow(base, i));
  }
  return result;
}
console.log(power(3, 3));

Alternatively, ES6 generators could be used:

function *power(base, exp){
  let prev = 1;
  for(var i=0; i<exp; i++){
    yield prev *= base;
  }
}

console.log([...power(3, 3)]);

Answer 2

Everything seems fine in your code except for the return value. Here is a slightly minified version of your code:

var task = (() => {
  var stack = [];
  function power(base, exponent) {
    return (exponent && (stack[--exponent] = base * power(base, exponent))) || 1;
  }
  power(3, 3);
  return stack;
});
console.log(task());

I personally don't prefer using recursive calls unless absolutely necessary.

In this scenario (assuming it's not just an exercise), there are alternative ways to achieve the same result. For example, using a classic for loop:

function power(base, exp){
  var result = [];
  for(var i=1; i<=exp; i++){
    result.push(Math.pow(base, i));
  }
  return result;
}
console.log(power(3, 3));

Alternatively, ES6 generators could be used:

function *power(base, exp){
  let prev = 1;
  for(var i=0; i<exp; i++){
    yield prev *= base;
  }
}

console.log([...power(3, 3)]);

Answer 3

Answer №2

Yes, the array is not returned, but rather the final calculated product. The desired result is actually stored in the stack after the function call completes.

However, it's considered poor practice to use a global variable that can be changed by a function. Instead, it's better to create what is known as a closure for this purpose and name it powers (plural, indicating an array will be obtained from it):

function powers(base, exponent) {
    // Creating an empty array named "stack"
    var stack = [];
    // Defining the recursive function
    function power(base, exponent) {
        // Base case 
        if (exponent === 0) {
            return 1;
        } else {
            stack[exponent - 1] = base * power(base, exponent - 1);
            return stack[exponent - 1];
        }
    }
    power(base, exponent);
    return stack;
}
console.log(powers(3, 3));

A more concise version:

function powers(base, exponent) {
    var stack = [];
    (function power(exponent) {
        return +!exponent || (stack[--exponent] = base * power(exponent));
    })(exponent);
    return stack;
}
console.log(powers(3, 3));

Answer 4

Yes, the array is not returned, but rather the final calculated product. The desired result is actually stored in the stack after the function call completes.

However, it's considered poor practice to use a global variable that can be changed by a function. Instead, it's better to create what is known as a closure for this purpose and name it powers (plural, indicating an array will be obtained from it):

function powers(base, exponent) {
    // Creating an empty array named "stack"
    var stack = [];
    // Defining the recursive function
    function power(base, exponent) {
        // Base case 
        if (exponent === 0) {
            return 1;
        } else {
            stack[exponent - 1] = base * power(base, exponent - 1);
            return stack[exponent - 1];
        }
    }
    power(base, exponent);
    return stack;
}
console.log(powers(3, 3));

A more concise version:

function powers(base, exponent) {
    var stack = [];
    (function power(exponent) {
        return +!exponent || (stack[--exponent] = base * power(exponent));
    })(exponent);
    return stack;
}
console.log(powers(3, 3));

JavaScript recursion used to generate arrays, according to the teachings of Codecademy

Answer №1

Answer №2

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