I need to create a JavaScript Promise that will not resolve until a specific condition is true. Let's say I have a 3rd party library, and I need to wait until a certain data condition exists within that library.
The scenario I am interested in is one where there is no way to know when this condition is satisfied other than by simply polling.
I can create a promise that waits on it - and this code works, but is there a better or more concise approach to this problem?
function ensureFooIsSet() {
return new Promise(function (resolve, reject) {
waitForFoo(resolve);
});
}
function waitForFoo(resolve) {
if (!lib.foo) {
setTimeout(waitForFoo.bind(this, resolve), 30);
} else {
resolve();
}
}
Usage:
ensureFooIsSet().then(function(){
...
});
I would normally implement a max poll time, but didn't want that to cloud the issue here.
A small variation would be to use a named IIFE so that your code is a little more concise and avoids polluting the external scope:
function ensureFooIsSet() {
return new Promise(function (resolve, reject) {
(function waitForFoo(){
if (lib.foo) return resolve();
setTimeout(waitForFoo, 30);
})();
});
}