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JavaScript Asynchronous Programming with JavaScript Understanding Promises Create a Promise

breakfastPromise.then(val => console.log(val) ) Is this a shorthand version of a function inside a method?

So Traditional Funtion name ( ) { functionbody }
On one line looks like: name ( ) { function body }

AnonymousFunction: // will need to be appended to a variable or 'something' in order to call it. ( ) { functionbody }
On one line looks like: ( ) { function body } is the same as ( ) => { function body } an anonymous function that takes no parameters:

an anonymous function that takes two or more parameters: (param 1, param 2) { functionbody} is the same as (param 1, param 2) => {functionbody}

Here's where I lose it - an anonymous function that takes one parameter ( 1 param) { function body } is the same as..... myparam => { function body }

so, where does 'myparam' come from and what is it? A parameter masquerading as a variable?

Then we take a step farther and get: breakfastPromise.then (val => console.log (val) ) .then is a method that can take one or two parameters. The second param is optional. The first param is automatically handled as 'resolve'. Why is there a function inside the then method? Where are the ( ) for the parameters and where are the { } for the function body? Can someone write the breakfastPromise.then in long hand? Why couldn't one just write breakfastPromise.then(console.log(resolve)); ?

Reggie Williams
Reggie Williams
Treehouse Teacher

Hey Kylie Soderblom in myparam is still a parameter of the function and just a placeholder in this situation. When written on one line it can just be done without parentheses. The function inside the then is run after the promise. Like the ; there are times when () and {} are recommended but not required in javascript

Thank you. For a seasoned coder, it most likely is second nature to know when one can skip () {}. But I'm still trying to make sense of when one is allowed to short cut. 1) Could you give me a long-hand example of myparam => { function body}?
Is it the same as let placeholder = (myparam) {function body} ? 2) And then why can't one shortcut and write breakfastPromise.then( console.log("whatever") ); I don't understand where the val comes from? Is it a placeholder or does it contain a value? I'm still struggling to read the arrow function correctly.

1 Answer

Reggie Williams
Reggie Williams
Treehouse Teacher

Hey Kylie Soderblom asking questions and seeking understanding as you are is how one becomes seasoned! myparam => { function body} is the same as let placeholder = (myparam) {function body} except that in the second option we can reuse the function because it is stored in the placeholder variable.

The promise returns a value when it is fulfilled. That's where val comes in but it must be passed into the function in then so it is in the correct scope.