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How to display a right triangle pattern in JavaScript

Ayush Trivedi


There are several patterns problems to solve, but in this shot, we will learn how to print a right triangle star (*) pattern with help of JavaScript. The right triangle pattern displays * in the form of a left triangle (right angled from the right side) on the screen or console.

Below is the shape which we will print using * in the console.

We have to use two for loops, where one will be a nested for loop. The outer loop will be for the row (height) of the triangle, and the nested loop will be used for the column.


We will write a program in JavaScript to print a star pattern in the form of a right triangle.

let n = 5;

for (let i = 1; i <= n; i++) {
  // printing spaces
  for (let j = 0; j < n - i; j++) {
    process.stdout.write(' ');
  // printing star
  for (let k = 0; k < i; k++) {

Code explanation

  • In line 1, we initialize a number that is a height of the triangle or the number of rows.

  • In line 3, we have have our first for loop, which will iterate over the row (height) of the triangle.

  • In line 5, we have our first nested for loop, which will print n - i spaces.

  • In line 4, the standard method of JavaScript is used, and process.stdout.write() will print the spaces.

  • In line 9, we have our second nested for loop, which will print i stars, where i is the number of times the external loop is executed.

  • In line 10, the standard method of JavaScript is used, and process.stdout.write() will print the star (*).

  • In line 12, we used console.log() with null, as it will change to a new line. We can use process.stdout.write('\n') to change the line.


We have successfully completed the task to print * in a form that looks like a right angle triangle. There can be different logics to print the same pattern.



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