Mastering TypeScript/

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Strong Typing and Basic Types

Strong Typing and Basic Types

Discover the distinction between strong typing in JavaScript and TypeScript and how TypeScript enforces rules for accurately using variables, functions, and objects.

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JavaScript is not strongly typed. It is a language that is very dynamic, as it allows objects to change their types, properties, and behavior on the fly. TypeScript, however, is strongly typed and, as such, will enforce rules that govern how we use variables, functions, and objects.

We will start with the concepts of strong typing or static typing, as it is also known. We will then move on to exploring some of the basic types that the language uses and how the language can detect what type a variable is based on how and where it is used within our code. We will then tackle the basics of function signatures and finally see how to import and use third-party JavaScript libraries.

Strong typing

Strong typing means that when we create a variable or define a parameter in a function, we specify what type it is. Once this type has been specified, we cannot change it. Loose typing is the exact opposite of this concept, and JavaScript is a loosely typed language.

As an example of loose typing in JavaScript, let’s take a look at the following code:

// Declare a variable called "test" and initialize it with a string value
console.log("Let's declare the variable 'test' with a string value\n");
var test = "a string";
// Log the value of "test" to the console
console.log("test = " + test);
console.log("\nWe can see the successful assignment of a string type to the 'test' variable.\n");
// Change the value of "test" to an integer
console.log("Now let's assign an integer value to 'test'\n");
test = 1;
console.log("test = " + test);
console.log("\nWe can see the successful assignment of an integer type to the 'test' variable. Notice that the type of the 'test' variable has changed from a string to an integer.\n");
// Change the value of "test" to a function
console.log("Now let's assign a function to 'test'\n");
test = function (a, b) {
  return a + b;
}
console.log("test = " + test + "\n");
console.log("This is how types work in JavaScript: variables can hold values of any data type, and the type of a variable can change during the execution of a program. This is in contrast to strongly-typed languages like TypeScript, in which variables must be explicitly declared with a specific data type and can only hold values of that type.");
Loose typing in JavaScript

  • On line 3 of this code snippet, we declare a local variable named test and assign it a string value. We then use the console.log function to print its value to the console. We display a message indicating that the assignment of a string value to test was successful.

  • On line 12, we assign an integer value of 1 to the test variable and print its value to the console. We display a message indicating that the assignment of an integer value to test was successful.

  • Finally, from line 24 — 26, we assign a function that takes two parameters, named a ...