Creating generic functions

Generics are a very useful way of creating flexible classes and functions. They are very similar to those used in C#. It's very useful to be used in more than one place.

We can create generic functions by adding angle brackets after the function names and enclosing datatypes, as in the following example:

function genericFunction<T>( arg: T ): T [] {
    let myGenericArray: T[] = [];
    myGenericArray.push(arg);
    return myGenericArray;
}

Note that the t inside the angle brackets (<t>) means that genericFunction() is of the generic type.

Let's see this in practice:

1. In your code editor, create a new file called generics.ts, and add the following code:

function genericFunction<T>( arg: T ): T [] {
    let myGenericArray: T[] = [];
    myGenericArray.push(arg);
    return myGenericArray;
}
let stringFromGenericFunction = genericFunction<string>("Some string goes here");
console.log(stringFromGenericFunction[0]);
let numberFromGenericFunction = genericFunction(190);
console.log(numberFromGenericFunction[0]);

Let's see what happens with our generic function.

2. Go back to your Terminal and type the following command:

tsc generics.ts

3. Now, let's execute the file with the following command:

node generics.js

We will see the following result:

Some string goes here
 190

Note that the compiler is able to identify the datatype that we are passing as the function argument. In the first case, we explicitly pass the argument as a string, and in the second case, we pass nothing.

Although the compiler is able to identify the type of argument that we are using, it is important to always determine what kind of data we are going to pass. For example:

let numberFromGenericFunction = genericFunction<number>(190);
console.log(numberFromGenericFunction[0]);