Ways to limit the scope of variables to prevent unauthorized changes

Question

Ways to limit the scope of variables to prevent unauthorized changes

Here is a variable and two functions for you to explore:

var a = [30,6,26,49,3,9,28];

The first function init(data) reverses the data twice and slices out the first element. The output will be an array without the last element.

The second function last(data) reverses the data once and slices out only the first element. The output will be an array with only the last element.

If you call both functions using the same variable like this:

init(a);
last(a);

You will notice that the output of the second function is unexpected due to the reverse operation inherited from the first function.

How can you use these functions sequentially while maintaining the original order of the variable?

javascript arrays function

Answer 1

Answer №1

Array.prototype.reverse will reverse the array itself without needing to clone it with .slice(). To avoid the need for reversing, you can use array.slice() directly like this:

var a = [30,6,26,49,3,9,28];

function initialize(data) {
  console.log("Init: " + data);
  var newDataSet = data.slice(0, -1);
  console.log(newDataSet);
  return newDataSet;
}

// Expected output:
// Init: 30,6,26,49,3,9,28
// [30, 6, 26, 49, 3, 9]

function showLast(data) {
  console.log("Last: " + data);
  var lastItem = data.slice(-1);
  console.log(lastItem);
  return lastItem;
}

// Expected output:
// Last: 30,6,26,49,3,9,28
// [28]

initialize(a);
showLast(a);

Check your browser console after running the code to view the results.

-1 has the same effect as data.length - 1.

Answer 2

Array.prototype.reverse will reverse the array itself without needing to clone it with .slice(). To avoid the need for reversing, you can use array.slice() directly like this:

var a = [30,6,26,49,3,9,28];

function initialize(data) {
  console.log("Init: " + data);
  var newDataSet = data.slice(0, -1);
  console.log(newDataSet);
  return newDataSet;
}

// Expected output:
// Init: 30,6,26,49,3,9,28
// [30, 6, 26, 49, 3, 9]

function showLast(data) {
  console.log("Last: " + data);
  var lastItem = data.slice(-1);
  console.log(lastItem);
  return lastItem;
}

// Expected output:
// Last: 30,6,26,49,3,9,28
// [28]

initialize(a);
showLast(a);

Check your browser console after running the code to view the results.

-1 has the same effect as data.length - 1.

Answer 3

Answer №2

Place this code snippet at the beginning of the function:

data = data.slice(0); // create a copy

Answer 4

Place this code snippet at the beginning of the function:

data = data.slice(0); // create a copy

Answer 5

Answer №3

Consider using reverse function following a slice operation. Slice creates a copy of the array.

var arr = [30,6,26,49,3,9,28];

function initialize(data) {
  document.write("Init: " + data);
  var modifiedData = data.slice(0, data.length - 1);
  document.writeln(" " + modifiedData);
  return modifiedData;
}

// Expected result:
// Init: 30,6,26,49,3,9,28
// [30, 6, 26, 49, 3, 9]

function getlast(data) {
  document.writeln("Last: " + data);
  var modifiedData = data.slice(data.length - 1, data.length);
  document.writeln(" " + modifiedData);
  return modifiedData;
}

// Expected result:
// Last: 30,6,26,49,3,9,28
// [28]

initialize(arr);
getlast(arr);

Answer 6

Consider using reverse function following a slice operation. Slice creates a copy of the array.

var arr = [30,6,26,49,3,9,28];

function initialize(data) {
  document.write("Init: " + data);
  var modifiedData = data.slice(0, data.length - 1);
  document.writeln(" " + modifiedData);
  return modifiedData;
}

// Expected result:
// Init: 30,6,26,49,3,9,28
// [30, 6, 26, 49, 3, 9]

function getlast(data) {
  document.writeln("Last: " + data);
  var modifiedData = data.slice(data.length - 1, data.length);
  document.writeln(" " + modifiedData);
  return modifiedData;
}

// Expected result:
// Last: 30,6,26,49,3,9,28
// [28]

initialize(arr);
getlast(arr);

Ways to limit the scope of variables to prevent unauthorized changes

Answer №1

Answer №2

Answer №3

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