Meteor Tracker guard

tracker.js

// Only trigger enclosing computation if the return value of 
// f is not EJSON.equals to the previuous return value
Tracker.guard = function(f) {
  if (Meteor.isServer || !Tracker.currentComputation) {
    return f();
  }

  let dep = new Tracker.Dependency(),
      curView = Blaze.currentView,
      tplFunc = Template._currentTemplateInstanceFunc;
  dep.depend();

  let value, newValue;
  Tracker.autorun(comp => {
    if (curView) {
      newValue = Blaze._withCurrentView(curView, () => {
        return tplFunc ? Template._withTemplateInstanceFunc(tplFunc, f) : f();
      });
    }
    else {
      newValue = f();
    }
    if (!comp.firstRun && !EJSON.equals(newValue, value)) {
      dep.changed();
    }
    value = EJSON.clone(newValue);
  });

  return newValue;
};

// Return a function which will always return the same
// value as f and changes value whenever f changes value,
// but is more efficient because it caches the value of f
// in a reactive variable.
Tracker.memo = function(f) {
  if (Meteor.isServer)
    return f;

  let value = new ReactiveVar(undefined, EJSON.equals),
      tracker = Tracker.nonreactive(() => Template.instance()) || Tracker,
      firstRun = true,
      comp = tracker.autorun(() => {
        if (!firstRun)
          value.set(f());
      });

  return () => {
    if (firstRun) {
      firstRun = false;
      comp._compute();
    }

    return value.get();
  };
};

// Starting work on tracking who triggered an autorun
let originalCompute = Tracker.Computation.prototype._compute;
Tracker.Computation.prototype._compute = function() {
  originalCompute.call(this);
  this.callers = [];
};

let originalInvalidate = Tracker.Computation.prototype.invalidate;
Tracker.Computation.prototype.invalidate = function() {

  if (!this._callers)
    this._callers = [];

  let e = new Error('dummy');
  let stack = e.stack.replace(/^[^\(]+?[\n$]/gm, '')
      .replace(/^\s+at\s+/gm, '')
      .replace(/^Object.<anonymous>\s*\(/gm, '{anonymous}()@')
      .split('\n');
  this._callers.push(stack);

  originalInvalidate.call(this);
};