prettyJson.js

function prettyJson(object, indent = 4, stack = []) {
  stack.push(object);

  let result = "{\n";

  let indentString = (new Array(indent+1)).join(" ");
  let indentEnd = (new Array(indent-3)).join(" ");

  let keys = Object.keys(object);
  keys.forEach((key, i) => {
    let value = object[key];

    result += indentString + `"${key}": `;
    if(typeof value === "object") result += stack.includes(value) ? "[Circular Object]" : prettyJson(value, indent + 4, stack);
    else if(typeof value === "string") result += `"${value}"`;
    else result += value;

    result += i === (keys.length - 1) ? "\n" : ",\n";
  });

  return result + indentEnd + "}"
}

// use as prettyJson({ a: 1, b: 2, c: '3', nested: { d: false, e: 4, j: 'string' } })