Convert Decimal to Octal in JavaScript

What You’ll Learn

Decimal-to-octal conversion turns a base-10 integer into a base-8 digit string (digits 0–7). This tutorial covers remainders, recursion, built-ins, a live preview, worked JavaScript examples, edge cases, and complexity.

📝 Problem & Approach

Given a nonnegative integer n, return its octal representation as a string (minimal digits, no leading zeros except for 0).

// 57 → remainders 1, 7 → reverse → "71"
// 64 → "100"
// 0  → "0"

Inputs & Outputs

Minimal workflow

function decimalToOctal(n) {  // n >= 0
  if (n === 0) return "0";
  const digits = [];
  while (n > 0) {
    digits.push(String(n % 8));
    n = Math.floor(n / 8);
  }
  return digits.reverse().join("");
}

Method comparison

🔮 Live Preview

Nonnegative integers in JavaScript safe range, using toString(8).

Press “Show octal” to convert.

Examples Gallery

Three complete JavaScript programs with Try it Yourself editors — remainder + reverse, recursive MSD-first, and built-in formatting. Click View Output to reveal sample console results.

function decimalToOctal(n) {
  if (n === 0) {
    return "0";
  }
  const digits = [];
  while (n > 0) {
    digits.push(String(n % 8));
    n = Math.floor(n / 8);
  }
  return digits.reverse().join("");
}

console.log("Octal equivalent:", decimalToOctal(57));
console.log("Octal equivalent:", decimalToOctal(0));

Octal equivalent: 71
Octal equivalent: 0

function printOctalRecursive(n) {
  if (n < 8) {
    return String(n);
  }
  return printOctalRecursive(Math.floor(n / 8)) + String(n % 8);
}

console.log("57 in octal:", printOctalRecursive(57));
console.log("0 in octal:", printOctalRecursive(0));

57 in octal: 71
0 in octal: 0

function toOctalBuiltin(n) {
  if (n < 0) {
    throw new Error("This helper expects a nonnegative integer");
  }
  return n.toString(8);
}

console.log(toOctalBuiltin(57));
console.log(toOctalBuiltin(0));
console.log((57).toString(8));       // same as above
console.log((57).toString(2));      // binary of 57
// 71 octal ↔ 111 001 binary (7=111, 1=001)

71
0
71
111001

🔎 Worked Walkthrough — n = 57

Trace the remainder method. Digits collect LSD-first, then reverse.

Reverse → 71. Check: 7 × 8 + 1 = 57.

⚖️ Facts Worth Knowing

Handy follow-ups interviewers sometimes ask.

🎯 Practice Problems

Try these variations to lock in the pattern.

Notes

⏱️ Time and Space Complexity

Here n is nonnegative and d is the number of octal digits.

💡 Best Practices