What does this type of const function expression do?

user_7384939 0
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I am having difficulties understanding what this line of code does/achieves. I don't understand the syntax and can't really find anything helpful on Google.

const uniqueId = (prefix?: string | undefined) => prefix};
typescript
2 Answers
const uniqueId = (prefix?: string | undefined) => prefix};

it is a TypeScript syntax. And it means that that function can receive zero or one argument and that argument should be either string type or undefined.

user_59074120
  • const means the variable is forced to stay as (prefix?: string | undefined) => prefix};.
  • uniqueId is the name of the constant variable.
  • The "prefix" in (prefix?: string | undefined) => prefix}; is the name of the argument.
  • ?: string | undefined means the argument is expected/must be a string, or undefined.
  • => prefix means it should just return the prefix immediately, which is just the rules of arrow functions.

Please note that the function is invalid, as the end has a }, but there is no starting {.

Edit:

Credit to @Dymtro Huz for this: The ? in the prefix?: string means that the parameter is not required/needed to call the function.

user_144163950
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