Nodejs check file exists, if not, wait till it exist

Question

I\'m generating files automatically, and I have another script which will check if a given file is already generated, so how could I implement such a function:

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Answer 1

Assuming you're planning on using Promises since you did not supply a callback in your method signature, you could check if the file exists and watch the directory at the same time, then resolve if the file exists, or the file is created before the timeout occurs.

function checkExistsWithTimeout(filePath, timeout) {
    return new Promise(function (resolve, reject) {

        var timer = setTimeout(function () {
            watcher.close();
            reject(new Error('File did not exists and was not created during the timeout.'));
        }, timeout);

        fs.access(filePath, fs.constants.R_OK, function (err) {
            if (!err) {
                clearTimeout(timer);
                watcher.close();
                resolve();
            }
        });

        var dir = path.dirname(filePath);
        var basename = path.basename(filePath);
        var watcher = fs.watch(dir, function (eventType, filename) {
            if (eventType === 'rename' && filename === basename) {
                clearTimeout(timer);
                watcher.close();
                resolve();
            }
        });
    });
}