An example showcasing the use of ES6 rest parameters for arguments

Question

An example showcasing the use of ES6 rest parameters for arguments

I'm having trouble grasping the JavaScript example provided below.

function containsAll(arr) {
  for (let k = 1; k < arguments.length; k++) {
    let num = arguments[k];
    if (arr.indexOf(num) === -1) {
      return false;
    }
  }
  return true;
}
let x = [2, 4, 6, 7];
console.log(containsAll(x, 2, 4, 7));
console.log(containsAll(x, 6, 4, 9));

When I run this code, it outputs 1 and 0 to the console.

I'm struggling to visualize how this function should operate.

Considering the call console.log(containsAll(x, 2, 4, 7)), the x should be substituted, resulting in console.log(containsAll(2, 4, 6, 7, 2, 4, 7)).
The function containsAll processes those numbers (2, 4, 6, 7, 2, 4, 7).
In the line,
```
for(let k = 1; k < arguments.length; k++)
```
, k should represent a new array [1, 2, 3, 4, 5, 6], depending on the argument length which corresponds to the length of arr (in this instance, the length is 7), correct?

Next, in

let num = arguments[k]; if (arr.indexOf(num) === -1) {return false;}

let num should take the value num = 1, is that right?

Subsequently, the if statement checks if 1 is present in the array, arr = [2, 4, 6, 7, 2, 4, 7]. If no match is found, it returns false. This process should continue for each number in the arr array, correct?

I'm simply trying to understand why the output is 1 for

console.log(containsAll(x, 2, 4, 7));

when I expected something like

[false, true, false, true, false, true]

.

javascript arrays

Answer 1

Answer №1

When using console.log(containsAll(x, 2, 4, 7)), make sure to replace the variable x with the actual values: console.log(containsAll(2, 4, 6, 7, 2, 4, 7)).

The correct values are [2, 4, 6, 7], 2, 4, 7

The function containsAll takes these numbers: (2, 4, 6, 7, 2, 4, 7).

It takes [2, 4, 6, 7], 2, 4, 7

When looking at this line,
for(let k = 1; k < arguments.length; k++)
, remember that k is representing the index in the arguments, not an array.

k is a number representing the index, not an array. The length is 4, and the array is a single element

In the next step,
let num = arguments[k]; if (arr.indexOf(num) === -1) {return false;}
, the variable num should be set to num = 1, correct?

num iterates over the remaining elements of arguments (2, 4, 7). Note the skipping of the first element with k=1.

The if statement checks if 1 is in the array, arr = [2, 4, 6, 7, 2, 4, 7]. If no match is found, it returns false. This process repeats for each number in the arr array.

The method returns as soon as it finds a match.

Concerns about the output of 1 when using
console.log(containsAll(x, 2, 4, 7));
arise from the fact that the execution stops when a return is encountered inside the method.

Execution halts at the moment of a return statement.

Answer 2

When using console.log(containsAll(x, 2, 4, 7)), make sure to replace the variable x with the actual values: console.log(containsAll(2, 4, 6, 7, 2, 4, 7)).

The correct values are [2, 4, 6, 7], 2, 4, 7

The function containsAll takes these numbers: (2, 4, 6, 7, 2, 4, 7).

It takes [2, 4, 6, 7], 2, 4, 7

When looking at this line,
for(let k = 1; k < arguments.length; k++)
, remember that k is representing the index in the arguments, not an array.

k is a number representing the index, not an array. The length is 4, and the array is a single element

In the next step,
let num = arguments[k]; if (arr.indexOf(num) === -1) {return false;}
, the variable num should be set to num = 1, correct?

num iterates over the remaining elements of arguments (2, 4, 7). Note the skipping of the first element with k=1.

The if statement checks if 1 is in the array, arr = [2, 4, 6, 7, 2, 4, 7]. If no match is found, it returns false. This process repeats for each number in the arr array.

The method returns as soon as it finds a match.

Concerns about the output of 1 when using
console.log(containsAll(x, 2, 4, 7));
arise from the fact that the execution stops when a return is encountered inside the method.

Execution halts at the moment of a return statement.

Answer 3

Answer №2

Currently, the output of your code shows `true` and `false` instead of 1 and 0. The reason why you're not getting an array like [false, true, false, true, false, true] is due to the `return` keyword used in the conditional `if` statement within your `for` loop.

Here's an alternative way to achieve the desired outcome:

function checkAll(arr) {
  let results = []
  for (let i = 1; i < arguments.length; i++) {
    let number = arguments[i];
    if (arr.indexOf(number) === -1) {
      results.push(0);
    } else {
      results.push(1);
    }
  }
  return results;
}

let y = [3, 5, 7, 8];
console.log(checkAll(y, 3, 5, 7)); //Expected Output [1, 1, 1]
console.log(checkAll(y, 7, 5, 9)); //Expected Output [1, 1, 0]

Answer 4

Currently, the output of your code shows `true` and `false` instead of 1 and 0. The reason why you're not getting an array like [false, true, false, true, false, true] is due to the `return` keyword used in the conditional `if` statement within your `for` loop.

Here's an alternative way to achieve the desired outcome:

function checkAll(arr) {
  let results = []
  for (let i = 1; i < arguments.length; i++) {
    let number = arguments[i];
    if (arr.indexOf(number) === -1) {
      results.push(0);
    } else {
      results.push(1);
    }
  }
  return results;
}

let y = [3, 5, 7, 8];
console.log(checkAll(y, 3, 5, 7)); //Expected Output [1, 1, 1]
console.log(checkAll(y, 7, 5, 9)); //Expected Output [1, 1, 0]

An example showcasing the use of ES6 rest parameters for arguments

Answer №1

Answer №2

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