correlation-id

Correlation id

Correlation id maintains a consistent id across asynchronous calls in node.js applications. This is extremely useful for logging purposes. For example within an API, each incoming request can be assigned an id that will be available in all function calls made processing that request, so we can see which requests caused errors.

Installation

npm i correlation-id --save

Compatibility

From v4 onwards this library requires node >=12.17.0. For older node versions use v3.x.

Simple example

As demonstrated by this example, all calls to getId() within the same withId() block will return the same id. The id can be supplied, otherwise a v4 uuid will be generated.

const correlator = require("correlation-id");

function printCurrentId(name) {
  console.log("%s id: %s", name, correlator.getId());
}

correlator.withId(() => {
  setTimeout(() => {
    printCurrentId("withId block 1, call 1");
  });
  setTimeout(() => {
    printCurrentId("withId block 1, call 2");
  }, 1000);
});

correlator.withId("my-custom-id", () => {
  setTimeout(() => {
    printCurrentId("withId block 2, call 1");
  }, 500);
});

// Output:
// withId block 1, call 1 id: 5816e2d3-6b90-43be-8738-f6e1b2654f39
// withId block 2, call 1 id: my-custom-id
// withId block 1, call 2 id: 5816e2d3-6b90-43be-8738-f6e1b2654f39

API

withId([id,] work)

Executes function work within a correlation scope and returns any result returned from work. Within work and any other function executions (sync or async) calls to getId() will return the same id. The id for the context may be set explicitly with the optional id parameter, otherwise it will be a v4 uuid. Calls to withId() may be nested.

correlator.withId(() => {
  console.log(correlator.getId()); // Writes a uuid to stdout
});
correlator.withId("my-custom-id", () => {
  console.log(correlator.getId()); // Writes 'my-custom-id' to stdout
});

bindId([id,] work)

Returns function work bound with a correlation scope. When work is executed all calls to getId() will return the same id. The id for the context may be set explicitly with the optional id parameter, otherwise it will be a v4 uuid. Arguments passed to the bound function will be applied to work.

const boundFunction = correlator.bindId((p1) => {
  console.log("p1 is", p1);
  console.log(correlator.getId());
});
boundFunction("foo"); // Writes 'p1 is foo' and then a uuid to stdout

const boundFunction2 = correlator.bindId("my-custom-id", (p1) => {
  console.log("p1 is", p1);
  console.log(correlator.getId());
});
boundFunction2("foo"); // Writes 'p1 is foo' and then 'my-custom-id' to stdout

getId()

Returns the id for the current correlation scope (created via withId or bindId). If called outside of a correlation scope returns undefined.

correlator.getId(); // Returns the current id or undefined

License

MIT

Changelog

4.0.0 (16th November 2020)

Change implementation to AsyncLocalStorage, no change to public API however minimum supported node version is not v12.17.0