Inverted Right-Angled Triangle Star Pattern in JavaScript

What You’ll Learn

The inverted right-angled triangle is the mirror of Program 1: same inner star loop, but the outer loop counts down so the widest line prints first. This tutorial covers reverse iteration, an equivalent forward-loop formula, a live preview, algorithm steps, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given a positive integer rows, print a left-aligned inverted right-angled triangle of * characters with rows lines.

// First 5 rows (conceptual shape)
// *****
// ****
// ***
// **
// *

Inputs & Outputs

Minimal workflow

for i from rows down to 1:
    for j from 1 to i:
        append "*"
    console.log(line)

Approach comparison

🔮 Live Preview

Choose a row count between 1 and 20 and draw the inverted triangle in the browser.

Press "Draw pattern".

Examples Gallery

Three complete JavaScript programs - countdown outer loop, prompt input, and a forward-loop equivalent with "*".repeat(stars). Click View Output to reveal sample console results, or Try it Yourself to run in the browser editor.

let rows = 5;

for (let i = rows; i >= 1; i--) {
  let line = "";
  for (let j = 1; j <= i; j++) {
    line += "*";
  }
  console.log(line);
}

*****
****
***
**
*

let rows = parseInt(prompt("Enter the number of rows:"), 10);
if (!Number.isFinite(rows) || rows < 1) {
  console.log("Please enter a whole number of rows >= 1.");
} else {
  for (let i = rows; i >= 1; i--) {
    let line = "";
    for (let j = 1; j <= i; j++) {
      line += "*";
    }
    console.log(line);
  }
}

Enter the number of rows: 7
*******
******
*****
****
***
**
*

let rows = 5;

for (let i = 1; i <= rows; i++) {
  const stars = rows - i + 1;
  console.log("*".repeat(stars));
}

*****
****
***
**
*

🔎 Worked Walkthrough — rows = 4

Trace each outer-loop value of i as it counts down, and count how many times the inner loop runs.

Total star prints: 4 + 3 + 2 + 1 = 10 = 4×5/2 - same total as the upright triangle of height 4.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

💡 Best Practices