Create an array

Constants

  const cars = [
    "Saab",
    "Volvo",
    "BMW"
  ];

  const cars = [];
  cars[0]= "Saab";
  cars[1]= "Volvo";
  cars[2]= "BMW";

  const MyArray = {
          'key_name_1': "Hello",
          'key_name_2': false,
          'key_name_3': 1234
        };

Variables

  var cars = [
    "Saab",
    "Volvo",
    "BMW"
  ];

  var cars = [];
  cars[0]= "Saab";
  cars[1]= "Volvo";
  cars[2]= "BMW";

  var MyArray = {
          'key_name_1': "Hello",
          'key_name_2': false,
          'key_name_3': 1234
        };

Array Length

  if (MyArray.count > 0)

Does array index exist?

if(typeof MyArray[index] === 'undefined')
{
    //Does not exist
}


if(typeof MyArray[index] !== 'undefined')
{
    //Does exist
}