Deprecation Guide for Use Ember getter and explicitly check for undefined

Deprecate support for getWithDefault in Ember's Object module (@ember/object) – both the function and the class method – because its expected behaviour is confusing to Ember developers.

• The API will only return the default value when the value of the property retrieved is undefined. This behaviour is often overlooked when using the function where a developer might expect that null or other falsey values will also return the default value.
• The native JavaScript Nullish Coalescing Operator ?? could be used to handle this case if we also take null as a falsey value to show the default value

Before:

import { getWithDefault } from '@ember/object';

let result = getWithDefault(obj, 'some.key', defaultValue);

After:

import { get } from '@ember/object';

let result = get(obj, 'some.key');
if (result === undefined) {
  result = defaultValue;
}

Using Nullish Coalescing Operator

We cannot codemod directly into the nullish coalescing operator since the expected behaviour of getWithDefault is to only return the default value if it is strictly undefined. The nullish coalescing operator accepts either null or undefined to show the default value.

The function getWithDefault will not return the default value if the provided value is null. The function will only return the default value for undefined:

let defaultValue = 1;
let obj = {
  nullValue: null,
  falseValue: false,
};

// Returns defaultValue 1, undefinedKey = 1
let undefinedValue = getWithDefault(obj, 'undefinedKey', defaultValue);

// Returns null, nullValue = null
let nullValue = getWithDefault(obj, 'nullValue', defaultValue);

// Returns obj's falseValue, falseValue = false
let falseValue = getWithDefault(obj, 'falseValue', defaultValue);

The nullish coalescing operator (??) will return the default value when the provided value is undefined or null:

let defaultValue = 1;
let obj = {
  nullValue: null,
  falseValue: false,
};

// Returns defaultValue 1, undefinedKey = 1
let undefinedValue = get(obj, 'undefinedKey') ?? defaultValue;

// Returns defaultValue 1, nullValue = 1
let nullValue = get(obj, 'nullValue') ?? defaultValue;

// Returns obj's falseValue, falseValue = false
let falseValue = get(obj, 'falseValue') ?? defaultValue;

For any given usage of getWithDefault, using nullish coalescing might work very well, but keep in mind that either null or undefined will return the default value.

Please review the deprecation RFC over at emberjs/rfcs for more details.