capabilities

index.js

const safeApply = Date.call.bind(Date.apply);
const randomName = () => Math.random().toString(36).slice(2).toLowerCase();

class RevokedCapabilityException extends Error {}

class Capability {
  constructor(behaviour, { name = randomName() } = {}) {
    this.behaviour = behaviour;
    this.name = Object.freeze([].concat(name));
  }

  run({ this: _this = null, arguments: args = [] } = {}) {
    return safeApply(this.behaviour, _this, args);
  }

  blame() {
    return this.name;
  }

  delegate({ name = randomName() } = {}) {
    let revoked = false;
    let self = this;
    return {
      revoke: () => {
        revoked = true;
      },
      capability: new Capability(function() {
        if (revoked) throw new RevokedCapabilityException();
        return self.run({ this: this, arguments });
      }, {
        name: [].concat(self.name, [name]),
      }),
    };
  }
}

module.exports = { Capability };

test.js

let Capability = require('./').Capability

let consoleCapability = new Capability((...args) => { console.log(...args); });

consoleCapability.run({ arguments: ["test", "capability"] });

let { revoke, capability: delegate } = consoleCapability.delegate();

delegate.run({ arguments: ["test", "delegate"] });
revoke();
try {
  delegate.run({ arguments: ["test", "revocation"] });
} catch(e) {
  console.log("revocation works");
}

consoleCapability.run({ arguments: ["test", "capability", "again"] });

console.log(delegate.blame());
console.log(consoleCapability.blame());