Typescript: Type signatures for any function.

Typescript: Type signatures for any function.

Today I will describe how to write type signatures for a wide range of javascript functions. This will help readers narrow types, increase reliability, type dependencies, and more. A type signature is like a blueprint for any given segment of code. It tells the compiler what things are. Well, typed programs are more reliable and they run faster.

Today I will describe how to write type signatures for a wide range of javascript functions. This will help readers narrow types, increase reliability, type dependencies, and more.

A type signature is like a blueprint for any given segment of code. It tells the compiler what things are. Well, typed programs are more reliable and they run faster. They also give the compiler a lot of additional information which helps us identify errors faster.


The “hello world” of function type signatures.

The most basic way to type a function is to declare the arguments and the return.

const returnArg = (arg:number):number => {
return arg
}

As you can see, the argument is number typed and the parenthesis has the same type declaration as the function body’s return statement.

If we change the return, we can change the type signature. this is the exact same function except it returns a string instead of a number.

const returnArg = (arg:number):string => {
return "yow"
}

Anything inside of the function body is typed the same as everything else in typescript. The function body can be treated as if it is its own stand-alone program.

Because of Typescript’s inference, it works almost the same if you don’t always type the return statement.

const returnArg = (first:number, second:number) => {
return first + second
}

In this example, we have not explicitly typed the function return, but since both args are explicit numbers the compiler is smart enough to know they cannot be anything else.


javascript typescript technology coding programming

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