Create 12 alphabet patterns in javascript

Practice makes a man perfect!
Let's create a few interesting alphabet patterns in javascript and understand loop in a better way.

What is alphabet patterns?

Alphabet patterns are a series of alphabets (Uppercase or Lowercase) which create some shape or geometrical figure.
Creating alphabet patterns or star patterns helps us to understand how to use and control loops.
Pattern questions are also asked in a freshers programming interview.
For explanation with real-time running code, check the article.

Pattern 1:

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

let n = 5; // you can take input from prompt or change the value
let string = "";
// External loop
for (let i = 1; i <= n; i++) {
  // printing characters
  for (let j = 0; j < i; j++) {
    string += String.fromCharCode(j + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 2:

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

let n = 5; // you can take input from prompt or change the value
let string = "";
// External loop
for (let i = 1; i <= n; i++) {
  // printing characters
  for (let j = 0; j < i; j++) {
    string += String.fromCharCode((i - 1) + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 3:

A
B C
D E F
G H I J
K L M N O

let n = 5;
let string = "";
let count = 0;
// External loop
for (let i = 1; i <= n; i++) {
  for (let j = 0; j < i; j++) {
    string += String.fromCharCode(count + 65);
    count++; // increment cause next alphabet
  }
  string += "\n";
}
console.log(string);

Pattern 4:

ABCDE
ABCD
ABC
AB
A

let n = 5;
let string = "";
// External loop
for (let i = 1; i <= n; i++) {
  for (let j = 0; j < n - i + 1; j++) {
    string += String.fromCharCode(j + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 5:

EDCBA
EDCB
EDC
ED
E

let n = 5;
let string = "";
// External loop
for (let i = 1; i <= n; i++) {
  for (let j = 0; j < n - i + 1; j++) {
    string += String.fromCharCode((n - 1 - j) + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 6:

EDCBA
DCBA
CBA
BA
A

let n = 5;
let string = "";
// External loop
for (let i = 1; i <= n; i++) {
  for (let j = 0; j < n - i + 1; j++) {
    string += String.fromCharCode((n - i - j) + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 7:

A
ABC
ABCDE
ABCDEFG
ABCDEFGHI

let n = 5;
let string = "";
// External loop
for (let i = 1; i <= n; i++) {
  // creating spaces
  for (let j = 0; j < n - i; j++) {
    string += " ";
  }
  // creating alphabets
  for (let k = 0; k < 2 * i - 1; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 8:

A
BCD
EFGHI
JKLMNOP
QRSTUVWXY

let n = 5;
let string = "";
let count = 0;
// External loop
for (let i = 1; i <= n; i++) {
  // creating spaces
  for (let j = 0; j < n - i; j++) {
    string += " ";
  }
  // creating alphabets
  for (let k = 0; k < 2 * i - 1; k++) {
    string += String.fromCharCode(count + 65);
    count++;
  }
  string += "\n";
}
console.log(string);

Pattern 9:

ABCDEFGHI
ABCDEFG
ABCDE
ABC
A

let n = 5;
let string = "";
// External loop
for (let i = 1; i <= n; i++) {
  // creating spaces
  for (let j = 1; j < i; j++) {
    string += " ";
  }
  // creating alphabets
  for (let k = 0; k < 2 * (n - i + 1) - 1; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 10:

A
ABC
ABCDE
ABCDEFG
ABCDEFGHI
ABCDEFG
ABCDE
ABC
A

let n = 5;
let string = "";
// Pyramid
for (let i = 1; i <= n; i++) {
  for (let j = 1; j < n - i + 1; j++) {
    string += " ";
  }
  for (let k = 0; k < 2 * i - 1; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
// Reverse Pyramid
for (let i = 1; i <= n - 1; i++) {
  for (let j = 1; j < i + 1; j++) {
    string += " ";
  }
  for (let k = 0; k < 2 * (n - i) - 1; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 11:

ABCDEFGHI
ABCDEFG
ABCDE
ABC
A
ABC
ABCDE
ABCDEFG
ABCDEFGHI

let n = 5;
let string = "";
// Reverse Pyramid
for (let i = 1; i <= n; i++) {
  for (let j = 1; j < i; j++) {
    string += " ";
  }
  for (let k = 0; k < 2 * (n - i + 1) - 1; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
// Pyramid
for (let i = 1; i <= n - 1; i++) {
  for (let j = 1; j < n - i; j++) {
    string += " ";
  }
  for (let k = 0; k < 2 * (i + 1) - 1; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
console.log(string);

Pattern 12:

A
AB
ABC
ABCD
ABCDE
ABCD
ABC
AB
A

let n = 5;
let string = "";
// Pyramid
for (let i = 1; i <= n; i++) {
  for (let k = 0; k < i; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
// Reverse Pyramid
for (let i = 1; i <= n - 1; i++) {
  for (let k = 0; k < n - i; k++) {
    string += String.fromCharCode(k + 65);
  }
  string += "\n";
}
console.log(string);