Benchmark: undefined vs typeof vs in vs hasOwnProperty

Script Preparation code:

var obj = { a: 1, b: 2, c: 3, d: 4, e: 5 };
var keys = new Array(4096 * 5);
for (let i = 0; i < keys.length; i += 1)
  keys[i] = Math.random().toString();

Tests:

undefined
for (let i = 0; i < 4096; i += 1) obj[keys[4096 * 0 + i]] === undefined;
typeof
for (let i = 0; i < 4096; i += 1) typeof obj[keys[4096 * 1 + i]] === "undefined";
in
for (let i = 0; i < 4096; i += 1) keys[4096 * 2 + i] in obj;
hasOwnProperty
for (let i = 0; i < 4096; i += 1) obj.hasOwnProperty(keys[4096 * 3 + i]);
bool
for (let i = 0; i < 4096; i += 1) !obj[keys[4096 * 4 + i]];

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
undefined
typeof
in
hasOwnProperty
bool

Fastest: N/A

Slowest: N/A

Latest run results:

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Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):

LLMs can make mistakes. Check important info.

**Benchmark Explanation**

The provided benchmark measures the performance of four different ways to check if a key exists in an object:

1. `in` operator
2. `hasOwnProperty` method
3. `typeof` operator with a string comparison
4. Boolean negation (`!`) with object comparison

The test case uses a large array of random keys and assigns them to the properties of a single object, allowing for a fair comparison between these different approaches.

**Comparison Options**

Here's a brief description of each option:

* `in`: The `in` operator checks if a property exists in an object by searching for it in the object's prototype chain. It returns a boolean value indicating whether the key is present.
* `hasOwnProperty`: This method checks if an object has a specific property as its own property (not inherited from the prototype chain). It returns a boolean value indicating whether the key is present.
* `typeof` with string comparison: In this case, the `typeof` operator is used to check if the type of the object at the given index is "undefined". This works because objects have an implicit `undefined` property when they are created. However, since JavaScript objects can inherit properties from their prototype chain, this approach may not always work as expected.
* Boolean negation with object comparison: In this case, a boolean expression is used to check if the value at the given index is falsy (i.e., `!`). This works because in JavaScript, an empty object (`{}`) is considered falsy.

**Pros and Cons**

Here's a brief summary of the pros and cons for each approach:

* `in`: Pros: Simple and straightforward. Cons: May not work as expected if the prototype chain is involved.
* `hasOwnProperty`: Pros: More robust than `in` since it checks only the own properties of the object. Cons: Can be slower due to method call overhead.
* `typeof` with string comparison: Pros: Fast and efficient for simple cases. Cons: May not work as expected if the prototype chain is involved or if the object is created using a different type of constructor (e.g., `Object.create()`).
* Boolean negation with object comparison: Pros: Simple and fast, but may not be immediately obvious how it works.

**Other Considerations**

In addition to the above considerations:

* For modern JavaScript engines, `in` should generally be the fastest approach since it uses a built-in operator.
* `hasOwnProperty` is often preferred over `in` because it provides more control and clarity in certain situations.
* The use of `typeof` with string comparison may not be relevant for newer versions of JavaScript (e.g., ECMAScript 2015+), which provide better support for object properties.

**Alternative Implementations**

Some alternative approaches to this benchmark include:

* Using the `Object.keys()` method and iterating over the resulting array to check if a property exists.
* Using the `Object.prototype.hasOwnProperty.call()` method to call both the prototype chain and the own properties of an object.
* Creating a custom function or utility that abstracts away these differences.

However, for most cases, the original four approaches (`in`, `hasOwnProperty`, `typeof` with string comparison, and Boolean negation) should provide sufficient performance and clarity.

Related benchmarks:

undefined vs typeof vs in vs hasOwnProperty (version: 0)

Object lookup performance

Comparing performance of: undefined vs typeof vs in vs hasOwnProperty vs bool

Created: 4 years ago by: Guest

Jump to the latest result

undefined

typeof

in

hasOwnProperty

bool

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

No previous run results

Autogenerated LLM Summary (model llama3.2:3b, generated one year ago):