javascript - Sync variables / Create an event listener for variables change value? -

suppose have 2 variables:

var connection1, connection2; connection1 = connection2 = false; 

and have 2 different functions connect remote node , change each variable true upon connection:

node1.on('open', function () {     connection1 = true;  }); node2.on('open', function () {     connection2 = true;  }); 

i want function run after both connections made, without checking other variable inside each on function.

how can create event listener trigger when both values set true without using setinterval ?

promise there save day.

// promise.all fulfill when promises resolved or 1 rejected promise.all(     [         new promise(             function(resolve, reject)             {                 node1.on("open", resolve);             }         ),         new promise(             function(resolve, reject)             {                 node2.on("open", resolve);             }         )     ] ) .then(     function()     {         console.log("connections 1 & 2 opened");     } ) .catch(     function(error)     {         console.log("error:", error);     } );