Datatypes in JS and relational databases


There are two principal differences between the way we model data in javascript and in a relational database.

Strict vs. weakly typed

In javascript the language determines the datatype at runtime. This means we can have code such as:

function Pizza(pizzaName, pizzaType, pizzaPrize, garlic) {
  this.pizzaName = pizzaName;
  this.pizzaType = pizzaType;
  this.pizzaPrize = pizzaPrize;
  this.garlic = garlic;

In the above example we do not specify that pizzaName and pizzaType are of type String or that pizzaPrize is of type Int and garlic of type boolean.

If we were creating a table in a database we would have to specify the datatypes like this:

  pizzaName TEXT,
  pizzaType TEXT,
  pizzaPrize INTEGER,
  garlic BOOLEAN);

Counting from zero or 1

In javascript the first object to be pushed onto the Array is number zero. So in a for loop we would write the following - counting the loop from zero:

function displayAllPizzas(pizzas) {
let pizzaString = "";
let pizzaArraySize = pizzas.length;
for (i = 0; i < pizzaArraySize; i++) {
pizzaString += pizza.pizzaName + ", "
+ pizza.pizzaType + ", "
+ pizza.pizzaPrize + ", "
+ pizza.garlic + "<br/>";
return pizzaString;

In a database the first id will normally be 1. So the first pizza in the table will be number 1.

Further reading: JavaScript Essentials: Types & Data Structures