JavaScript Program to Print Character Pattern

Printing a character pattern involves generating and displaying a structured arrangement of characters, often in a specific geometric shape such as a triangle or square. This process typically includes using loops to systematically place characters in rows and columns based on given rules.

Here are some common approaches:

Using Nested Loop

Using nested loops, iterate over rows and columns, incrementally printing based on row number. The outer loop controls rows, inner loop controls columns, printing Character for each column up to the row number.

Example: The function myPatternFunction iterates over rows, incrementally printing Characters based on row number, achieving a pattern with increasing lengths per row.

function myPattern(rows, startCharacter) {
    const startCharCode = startCharacter.charCodeAt(0);
    for (let i = 0; i < rows; i++) {
        let pattern = '';
        for (let j = 0; j <= i; j++) {
            pattern += String
                .fromCharCode(startCharCode + j);
        }
        console.log(pattern);
    }
}

myPattern(5, 'A');

A
AB
ABC
ABCD
ABCDE

Using Recursion

Recursively print a character pattern by appending a Character in each recursive call, incrementing the row number. The base case returns if the row exceeds the limit. Each call prints the pattern with an additional Character compared to the previous row.

Example: We will print a pattern of Character with increasing length per row, up to the specified number of rows (in this case, 5), using recursion.

function myPattern(rows, row = 1,
    pattern = '') {
    if (row > rows) return;
    pattern += String.fromCharCode(64 + row) + ' ';
    console.log(pattern);
    myPattern(rows, row + 1, pattern);
}

myPattern(5);

A 
A B 
A B C 
A B C D 
A B C D E 

Using Array and Join

This approach builds a character pattern using nested loops and arrays. Each line is created as an array of characters, joined into a string, and stored in another array. The array of lines is then printed. Character codes are cycled from 'A' to 'Z'.

Example : In this example the printPattern3 function generates a pattern of increasing lines of alphabetic characters, resetting from 'Z' to 'A' if needed. It prints each line, forming a triangular pattern of letters for `n` lines.

function printPattern3(n) {
    let charCode = 65;
    let arr = [];
    for (let i = 0; i < n; i++) {
        let line = [];
        for (let j = 0; j <= i; j++) {
            line.push(String.fromCharCode(charCode++));
            if (charCode > 90) charCode = 65;
        }
        arr.push(line.join(''));
    }
    arr.forEach(line => console.log(line));
}

printPattern3(5);

A
BC
DEF
GHIJ
KLMNO

Using String Repeat Method

Using the string repeat method, generate character patterns efficiently by repeating a specified character for each row. This method calculates the number of characters needed per row and prints the pattern in a loop.

Example : In this example The repeatPattern function logs increasing repetitions of a character char up to n times

function repeatPattern(n, char) {
    for (let i = 1; i <= n; i++) {
        console.log(char.repeat(i));
    }
}

repeatPattern(5, 'A');

A
AA
AAA
AAAA
AAAAA