javascript箭头函数（）=>（）是什么意思？

Question

I came across this syntax. Could any one explain what getArg1ListInfo:()=>(object.freeze(arg1)) means

function foo (arg1,arg2) {
    let retval = {
        service:service
    }
    if(arg1) {
        retval.getArg1InfoHelper = () => {
            return {
                 subArg : "string",
                 getArg1ListInfo:()=>(object.freeze(arg1))
            }
        }
     }
     return retval
}

Answer 1

()=>(object.freeze(arg1))

is equivalent to

()=>object.freeze(arg1)

The brackets seem to be confusing you. They are not syntax, they are just redundant.

---

A reason one might use brackets in this way is for returning object literals. To use @Phil's example from the comments,

() => ({foo: 'bar'})

In this example, the brackets are used to avoid a syntax error. It's possible that the person who wrote your example code has come against this problem in the past, and has formed a habit.

Answer 2

The ()=>() syntax is a shorthand way of defining a single-statement function, where the result of that statement is returned as the result of the arrow function.

In the case of getArg1ListInfo:()=>(Object.freeze(arg1)) , when getArg1ListInfo gets called, it will return the result of object.freeze(arg1) .

So for example:

var result = foo({},{}).getArg1InfoHelper().getArg1ListInfo()

Will mean that result contain the result of object.freeze(arg1) . According to the MDN docs , this means that result would contain the object arg1 .

Answer 3

(params) => (expression)

is the equivalent of

function (params) { return expression;}

source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/Arrow_functions