How does the new promise API work?

[espruino-discuss]

Posted at 2016-08-06 by luwar

I would like to use the new Promise API introduced in 1v86 but I'm not able to get even the simplest scenarios to work.
Should the Espruino promises work like the normal ES6 promises?

The following code should output 1 1 2 4 but does 1 1 1 1. A bug or a feature? ;-)

var p = new Promise( function(resolve) { resolve(1); });

p.then( function(value) {
        console.log(value);  // 1
        return value + 1;
}).then( function(value) {
        console.log(value);  // 2
        return new Promise( function( resolve ) { resolve( 4 ); } );
}).then( function( value ) {
        console.log( value ); // 4
} );

p.then(function(value) {
        console.log(value); // 1
});

[gfwilliams]

Posted at 2016-08-07 by @gfwilliams

Ahh, yes - i'd say that's a bug then. I'll file an issue for it... I'm amazed nobody else spotted that.

The whole resolve reject thing works, but I bet it doesn't cope with stacking thens - which is kind of the point :)

[espruino-discuss]

Posted at 2016-09-04 by fraser

Hi Gordon

Did this issue get resolved in an update?

[gfwilliams]

Posted at 2016-09-05 by @gfwilliams

Not yet I'm afraid. I was on holiday immediately after that and then again last week, so I spent most of my time playing catch-up on e-mails and making sure the Puck.js stuff was moving along.

[gfwilliams]

Posted at 2016-09-05 by @gfwilliams

The relevant issue is this one: espruino/Espruino#894

I just had a quick stab at this but it'll need a bit more time to get working for multiple calls of p.then. I'd been assuming that it always chained calls, but you can actually call two things at the same time with it.