continuation-local-variable

continuation-local-variable

Variables scoped by a chain of asynchrounous calls

How it works

    const Variable = require('continuation-local-variable');

    const User = Variable.create('user');
    User.set("Moe");

    setTimeout(function() {
      print(Variable.find('user').value());  // prints 'Moe'
    }, 1000);

    // User name will be 'Larry' for the chain of async operations
    // starting with `setTimeout`
    User.set("Larry"); sets
    setTimeout(function() {
      print(Variable.find('user').value());  // prints 'Larry'
      // http request
      axios.get('http://www.github.com').then(() => {
        print(Variable.find('user').value());  // still prints 'Larry'
      })
    }, 500);

    // User name is 'Curly' for the async chain starting with the next `setTimeout`
    User.set("Curly");
    setTimeout(function() {
      print(Variable.find('user').value());  // prints 'Curly'
      process.nextTick(() => {
        print(Variable.find('user').value());  // prints 'Curly'
      });
    }, 500);

Requirements

NodeJS 8.9 or above

API Reference

Variable.create(variableName)

Creates a new async scoped variable

Variable.find(variableName)

Finds an existing variable

Variable.set(value)

Sets the value of the variable. This value will hold for the duration of the next asynchronous call chain.

Variable.get()

Returns the value of this variable.