Javascript wait until function is defined

Question

I want to :

wait until a function A is defined (it's in a file loaded asynchronusly)
then run function B
and i'd like to create a generic wrapper for that, so that i can directly make something like waitFor(functionToWait, functionToExecute)
- i have a result for part 1 & 2, but it's based on setTimeout/setInterval, but i'd like to know if there would be a more elegant way (something like a watcher on the waited function)
- and i have no idea on the second part, especially how to use a string parameter to convert it into a function reference.

Thanks

`it's in a file loaded asynchronusly` Can you explain this a bit more? Can you show the code that loads the file? — CertainPerformance, Dec 12 '18 at 08:01
Give the `script` tag a `load` listener, which will fire once the script has been downloaded, parsed, and run. Have the other script assign the function to something global, and then when the `load` event fires, you'll be able to call that global function. — CertainPerformance, Dec 12 '18 at 08:39

score 2 · Answer 1 · answered Dec 12 '18 at 08:10

My answer is a combination of the answers from: What is the JavaScript version of sleep()? and: How to check if function exists in JavaScript?

    function sleep(ms) {
        return new Promise(resolve => setTimeout(resolve, ms));
    }

    async function demo(cb) {
        while(typeof A !== "function") {
            await sleep(1000);
        }
        cb();
    }

    demo(function() { console.log("function A exists"); });

    var A = function() { };

I don't quite get why isn't main processes blocked by awaiting sleepover — RomanistHere, Apr 30 '21 at 14:26

Javascript wait until function is defined

1 Answers1