具有其他函数的返回值作为变量的函数，是否异步？

Question

I have the following:

var module = {}
module.setDate = function() {
    var d = new Date();
    return d;
}

Say I now have:

function logDate(){
   var date = module.setDate();
   console.log(date)
   console.log('finished')
}

Is the setting of var date to the return value of module.setDate() synchronous or asynchronous? Could the console ever look like:

undefined
'finished'

Answer 1

I think you're confusing a function call with a constructor.

var d = new Date();

This will create a Date object immediately, that that's what your function is returning.

On the other hand, if your function were

var module = {}
module.setDate = function() {
    return function() {
        var d = new Date();
        return d;
    }
}

This would be asynchronous, but not parallelly executed. The execution of the function you return would wait until you call the function.

function logDate(){
   var date = module.setDate();
   console.log(date() /* <--- need these parens, now! */)
   console.log('finished')
}

In order to truly execute in parallel, which I think it what you are trying to ask by saying "asynchronous", then I'd suggest reading up on one of these links.

• Parallel JavaScript Code
• http://ejohn.org/blog/web-workers/
• https://adambom.github.io/parallel.js/