Nested Statements in JavaScript (OCR A Level Computer Science): Revision Note

Nested Statements in JavaScript

• Nesting is putting one block of code within another

• This is commonly done with if statements and loops

• Nested if statements refer to the practice of including one or more conditional statements inside the block of another conditional statement

• These nested structures allow you to create more complex decision-making logic by evaluating multiple conditions and handling various scenarios within your code

• Nested loops refer to the practice of including one or more loops inside the block of another loop

• These nested structures allow you to iterate over multiple sets of data and create more complex patterns of repetition within your code

Nested If statements in JavaScript

• If statements can be nested within each other to handle more intricate conditions and decision-making:

Nested if statement in JavaScript

Nested loops in JavaScript

• The syntax of nested loops involves placing one loop (for loop, while loop, etc.) inside the block of another loop:

for (let i = 0; i < outerArray.length; i++) {
  // Code block for outer loop

  for (let j = 0; j < innerArray.length; j++) {
    // Code block for inner loop

    // More nested loops if needed
  }

  // More code after inner loop
}

Example: nested for loops

Nested for loop in JavaScript showing a 2D array with each item in the array being added together to find the sum of the whole array

• After the first iteration sum=1 as it's only added the 1st element which is 1

• After the 2nd iteration sum=3 as it's added the 2nd element (2) to 1

• After the 3rd iteration sum=6 as it's added the 3rd element (3) to the 1 and 2

• After the 4th iteration sum=10 as it's added the 4th element (4) to the 1, 2 and 3

• The algorithm continues working its way through the rest of the 2nd row and then moves on to the 3rd

Example: nested while loops

• This code below does the same as the code above but utilises while loops rather than for loops:

const matrix = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9]
];

let i = 0;
while (i < matrix.length) {
  let j = 0;
  while (j < matrix[i].length) {
    console.log(matrix[i][j]);
    j++;
  }
  i++;
}