I've been writing a bunch of shell-script-like node scripts lately. These
mostly call a series of async functions that take the usual function
(error, data) { ... } callback, and generally they handle any error along
the way by logging it and exiting. Here's a naive example using aws-sdk to
make a couple EC2 API calls in serial
var AWS = require("aws-sdk");
var ec2 = new AWS.EC2.Client();
ec2.runInstances({ ... }, function (error, runInstancesResponse) {
if (error) {
console.log(error);
process.exit(1);
} else {
// ... get the instanceIds from response as input to createTags
ec2.createTags({ ... }, function (error, createTagsResponse) {
if (error) {
console.log(error);
process.exit(2);
} else {
// ... do further processing ...
}
});
}
});
As you can see a lot of the total lines are just totally boilerplate if
(error) barf. Since we've got a functional language here, pretty easy to
encapsulate that, e.g. with this
Function.prototype.xie = Function.prototype.exitIfError = function
(exitCode) {
var f = this;
return function (error, data) {
if (error) {
console.log(error);
process.exit(exitCode || 1);
} else {
f.call(this, data);
}
};
}
our code collapses to just
ec2.runInstances({ ... }, function (runInstancesResponse) {
// ... get the instanceIds from response as input to createTags
ec2.createTags({ ... }, function (createTagsResponse) {
// ... do further processing ...
}.xie(2));
}.xie(1));
Which feels a lot more readable to me. Is there precedent for this
technique? A name for it? Any well known modules that implement it? Any
obvious horrible side effects? Clearly not applicable to sophisticated
error handling, but for this basic "it all works or just give up" kind of
thing it seems handy. Could add "abort if error", "throw if error", "emit
if error" flavors as well.
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