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JavaScript

Posted by Travis Fulton
Travis Fulton
13,620 Points

I don't understand how or why 'value' is working here 

var calcPromise = new Promise(function(resolve, reject){
  setTimeout(function(){
    resolve(1 + 1);
  }, 1000);
});

calcPromise.then(function(value){
   console.log("the answer is ", value);
});

It seems like 'value' should have been declared somewhere, but it seems like it's magically just returning the result

3 Answers

Steven Parker
Steven Parker
243,656 Points
Steven Parker
Steven Parker
243,656 Points

You are declaring "value" as the name of the parameter used by your then function:

calcPromise.then(function(value) {

The promise passes the actual value when it calls that function.

Travis Fulton
Travis Fulton
13,620 Points
Travis Fulton
Travis Fulton
13,620 Points

I meant I'd expect 'value' to have been declared as a variable for it to work like this. I see that it's declared as a parameter, but I don't see how it 'knows' that it's assigned to the result of the math equation in the setTimeout. Thanks.

Steven Parker
Steven Parker
243,656 Points
Steven Parker
Steven Parker
243,656 Points

The "value" parameter is passed to the function you registered with then when your promise calls the "resolve" function and passes the math result to it as the argument.

Travis Fulton
Travis Fulton
13,620 Points
Travis Fulton
Travis Fulton
13,620 Points

Ah! Thanks.