typescript - (): meaning in javascript function -


i looking @ piece of code in react application: 

export const clickoptoutmessage = (): clickoptoutmessage => ({   type: click_opt_out_message, });

what (): do? having trouble googling due fact it's bunch of characters.

i'll try explain step step (sorry if know except ending, people may learn new)

() => { /** function body goes here **/ }

is arrow function

() => {}  //basically equals: (function () {}).bind(this)

it have context written.

in typescript can write function return type, this:

function(): number {   return 2; }

so, know since arrow function function different syntax - (): type return type!

export const clickoptoutmessage = (): clickoptoutmessage => ({   type: click_opt_out_message, });

somewhere in code looked at, there piece:

const click_opt_out_message = "click_opt_out_message"; // value can differ in code observed  type clickoptoutmessage = {   type: "click_opt_out_message" }

as can see, 

(): clickoptoutmessage

pretty tells type of return value.


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