Inverted Center-Aligned Pyramid Star Pattern in JavaScript

What You’ll Learn

An inverted centered pyramid reuses Program 5’s formulas — (rows - i) spaces and (2 * i - 1) stars — but runs the outer loop from rows down to 1 so the widest row prints first. This tutorial covers reverse iteration, a live preview, algorithm steps, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given a positive integer rows, print an inverted center-aligned pyramid of * characters with rows lines (widest first).

// First 5 rows (spaces shown as ·)
// *********
// ·*******
// ··*****
// ···***
// ····*

Inputs & Outputs

Minimal workflow

for i from rows down to 1:
    for j from 1 to (rows - i):
        append " "
    for k from 1 to (2 * i - 1):
        append "*"
    console.log(line)

Approach comparison

🔮 Live Preview

Choose a height between 1 and 14 and draw the inverted centered pyramid in the browser.

Press "Draw pyramid".

Examples Gallery

Three complete JavaScript programs — countdown nested loops, prompt input, and a " ".repeat / "*".repeat shortcut. 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 <= rows - i; j++) {
    line += " ";
  }
  for (let k = 1; k <= 2 * i - 1; k++) {
    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 <= rows - i; j++) {
      line += " ";
    }
    for (let k = 1; k <= 2 * i - 1; k++) {
      line += "*";
    }
    console.log(line);
  }
}

Enter the number of rows: 4
*******
 *****
  ***
   *

let rows = 5;

for (let i = rows; i >= 1; i--) {
  console.log(" ".repeat(rows - i) + "*".repeat(2 * i - 1));
}

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

🔎 Worked Walkthrough — rows = 4

Trace spaces, stars, and characters per row as i counts down from 4 to 1.

Star total: 7+5+3+1 = 16 = 4² — same as Program 5, different print order.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

Total stars = rows²; each row also prints up to Θ(rows) spaces. Same as Program 5.

💡 Best Practices