How to check if a variable is an object in JavaScript?

function isObject(variable) {
  return (
    typeof variable === 'object' &&
    variable !== null &&
    !Array.isArray(variable)
  );
}

function isObject(variable) {
  return variable === Object(variable);
}

function isObject(variable) {
  return Object.prototype.toString.call(variable) === '[object Object]';
}

Object.prototype.toString.call({})   // '[object Object]'
 
Object.prototype.toString.call([])   // '[object Array]'
 
Object.prototype.toString.call(null) // ️'[object Null]'
 
Object.prototype.toString.call('')   // ️'[object String]'
 
Object.prototype.toString.call()     // '[object Undefined]'