isJSON.js

/**
 * Checks if a given input is a valid JSON string or an object.
 *
 * @param {string|object} input - The input to be checked, which can be a JSON string or an object.
 * @returns {boolean} - Returns true if the input is a valid JSON string or an object, false otherwise.
 */
function isJSON(input) {
  // Check if the input is not a string
  if (typeof input !== 'string') {
    // Check if the input is already an object
    if (typeof input === 'object' && input !== null) {
      return true;
    }
    return false;
  }
  
  try {
    // Try parsing the input string as JSON
    const obj = JSON.parse(input);
    if (typeof obj === 'object' && obj !== null) {
      return true;
    }
    return false;
  } catch (err) {
    // If parsing fails, input is not a valid JSON string
    return false;
  }
}

function isJSON_test() {
  const myObj = { name: 'John', age: 30 };
  const myJSON = JSON.stringify(myObj);

  console.log(isJSON(myObj)); // true
  console.log(isJSON(myJSON)); // true
  console.log(isJSON('not JSON')); // false

}