Does JavaScript promise create memory leaks when not rejected or resolved?
I'm in a situation where I need execute async functions in "parallel", and continue program execution with the best result. Thus I wrote something like this :
var p = [];
for (var i = 0; i < 10; ++i) (function (index) {
p.push(new Promise(function (resolve, reject) {
setTimeout(function () {
var success = Math.random() > 0.7;
console.log("Resolving", index, "as", success ? "success" : "failure");
success && resolve(index);
}, Math.random() * 5000 + 200);
}));
})(i);
Promise.race(p).then(function (res) {
console.log("FOUND", res);
}).catch(function (err) {
console.log("ERROR", err);
});
Now, I'm wondering if this is good practice when working with promises? Is not resolving or rejecting them more often then anything create memory leaks? Are they all eventually GC'ed every time?
The only reason this will leak is because p is a global. Set p = null; at the end, or avoid using a global variable:
var console = { log: function(msg) { div.innerHTML += msg + "<br>"; }};
Promise.race(new Array(10).fill(0).map(function(entry, index) {
return (function(index) {
return new Promise(function(resolve) {
setTimeout(function() {
var success = Math.random() > 0.7;
console.log((success? "R":"Not r") + "esolving "+ index +".");
success && resolve(index);
}, Math.random() * 5000 + 200);
});
})(index);
})).then(function (res) {
console.log("FOUND: " + res);
}).catch(function (err) {
console.log("ERROR: " + err);
});<div id="div"></div>