Repeating-Letter Alphabet Pattern in JavaScript

What You’ll Learn

Row 1 is one A, row 2 is two Bs, row 3 three Cs, and so on: A, BB, CCC, DDDD, EEEEE. Contrast Program 1, where letters change inside each row. Here, the row letter stays the same and only the count grows. Next up: Program 10 reverses the letter order. Includes a live preview, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given a positive integer rows, print a left-aligned repeating-letter alphabet pattern: each row prints one letter repeated row times (A, BB, CCC when rows = 5).

// First 5 rows (conceptual shape)
// A
// BB
// CCC
// DDDD
// EEEEE

Inputs & Outputs

Minimal workflow

base = "A".charCodeAt(0)
for row from 1 to rows:
    ch = String.fromCharCode(base + row - 1)
    repeat ch exactly row times (inner loop or ch.repeat(row))
    console.log(line)

Approach comparison

🔮 Live Preview

Choose 1–26 rows and draw the repeating-letter alphabet triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete JavaScript programs — fixed A–E, user-chosen row count, and a ch.repeat(row) shortcut. Click View Output to reveal sample console results, or Try it Yourself to run in the browser editor.

const rows = 5;
const base = "A".charCodeAt(0);

for (let row = 1; row <= rows; row++) {
  const ch = String.fromCharCode(base + (row - 1));
  let line = "";
  for (let j = 0; j < row; j++) {
    line += ch;
  }
  console.log(line);
}

A
BB
CCC
DDDD
EEEEE

const rowsInput = prompt("Enter the number of rows (max 26):");
let rows = parseInt(rowsInput, 10);
rows = Math.max(1, Math.min(rows, 26));

const base = "A".charCodeAt(0);

for (let row = 1; row <= rows; row++) {
  const ch = String.fromCharCode(base + (row - 1));
  let line = "";
  for (let j = 0; j < row; j++) {
    line += ch;
  }
  console.log(line);
}

Enter the number of rows (max 26): 4
A
BB
CCC
DDDD

const rows = 5;
const clampedRows = Math.max(1, Math.min(rows, 26));
const base = "A".charCodeAt(0);

for (let row = 1; row <= clampedRows; row++) {
  const ch = String.fromCharCode(base + (row - 1));
  console.log(ch.repeat(row));
}

A
BB
CCC
DDDD
EEEEE

🔎 Worked Walkthrough — rows = 5

Trace each outer-loop row value and see how the letter formula and repetition count produce each printed line.

Highlight rows 1, 3, and 5: A ×1 → A; C ×3 → CCC; E ×5 → EEEEE. Total letter prints: 1 + 2 + 3 + 4 + 5 = 15 = 5×6/2.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

For n rows you print 1+2+…+n = n(n+1)/2 characters, so total work is O(n²).

💡 Best Practices