Deprecation Guide for Function as test in Ember.deprecate, Ember.warn, Ember.assert

Calling Ember.deprecate, Ember.warn or Ember.assert with a function as test argument is deprecated.

You can no longer pass arguments of type function to these methods. Following calls will trigger deprecations:

const message = 'Test message.';
const options = { id: 'test', until: '3.0.0' };

// passing function
Ember.deprecate(message, function() {
  return true;
}, options);

const myConstructor = {}.constructor;

// passing constructor (also a function)
Ember.warn(message, myConstructor, options);

// passing function with double arrow syntax
Ember.assert(message, () => true, options);

Demo.

Refactoring

You have 3 options to refactor second argument from function to boolean:

1. Use IIFE.
2. Use !!Constructor for constructors.
3. Pass boolean directly instead of wrapping it in function.

Example:

// ... message, options omitted for brevity

// passing IIFE (1)
Ember.deprecate(message, (function() {
    return true;
})(), options);

const myConstructor = {}.constructor;

// passing !!constructor (2)
Ember.warn(message, !!myConstructor, options);

// passing boolean directly (3)
Ember.assert(message, true, options);

Demo.

In a future version functions will be treated as truthy values instead of being executed.