Learning TypeScript 2.x - Second Edition

Trailing commas in function arguments

Trailing commas are the commas that are used after the last argument of a function. Using a comma after the last parameter of a function can be useful because it is very common for programmers to forget to add a comma when they modify an existing function by adding additional parameters.

For example, the following function only takes one parameter and doesn't use trailing commas:

function greetWithoutTralingCommas( 
    name: string 
): string { 
    return `Hi! ${name}`; 
} 

After some time, we might be required to add a parameter to the preceding function. A common mistake is to declare the new parameter and forget to add a comma after the first parameter:

function updatedGreetWithoutTralingCommas( name: string ...