Benchmark: Typeof x === 'undefined' vs x === undefined (test without syntax error)

Script Preparation code:

var x = undefined;

Tests:

Typeof check
typeof x === 'undefined';
Strict equality
x === undefined;

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
Typeof check
Strict equality

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: one year ago)

User agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.84 Safari/537.36

Browser/OS: Chrome 99 on Windows

View result in a separate tab

Test name	Executions per second
Typeof check	795415936.0 Ops/sec
Strict equality	310433248.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's break down the provided benchmark and explain what's being tested, along with the pros and cons of each approach.

**Benchmark Definition**

The benchmark is testing two different ways to check if a variable `x` is `undefined`. The two approaches are:

1. `typeof x === 'undefined'`
2. `x === undefined`

Both approaches seem to achieve the same goal, but they differ in their syntax and implementation details.

**Options Compared**

* `typeof x === 'undefined'`: This approach uses the `typeof` operator to check the type of `x`. The `typeof` operator returns a string representing the type of the variable, such as `'object'`, `'number'`, or `'string'`. In this case, it checks if the type is `'undefined'`.
* `x === undefined`: This approach uses strict equality (`===`) to check if `x` has a value equal to `undefined`.

**Pros and Cons**

* **`typeof x === 'undefined'`**:
	+ Pros: More explicit and clear in its intention. It's easier to read and understand, especially for developers familiar with JavaScript.
	+ Cons: Can be slower due to the overhead of the `typeof` operator.
* **`x === undefined`**:
	+ Pros: May be faster since it avoids the overhead of the `typeof` operator.
	+ Cons: Less explicit in its intention. It may lead to confusion if not understood correctly.

**Other Considerations**

In modern JavaScript, both approaches are considered valid and widely supported. However, it's worth noting that older browsers or environments might have issues with the `typeof` operator or strict equality checks.

**Library Usage**

There is no explicit library mentioned in the benchmark definition or test cases. The only mention of a library is in the individual test case:

* "Benchmark Definition": "typeof x === 'undefined';"

This seems to be a typo, and it's likely meant to reference the `typeof` operator instead.

**Special JS Features/Syntax**

There are no special JavaScript features or syntax mentioned in the benchmark definition or test cases. The code snippets only use standard JavaScript operators (`===`, `var`) and does not include any advanced features like async/await, generators, or arrow functions.

**Alternatives**

Other alternatives for checking if a variable is `undefined` might include:

* Using an empty object (`{}`) as the expected value: `{ x: undefined }`
* Using the `Object.is()` method (available in modern browsers and Node.js)
* Using a library like Lodash, which provides a `isUndefined()` function

Keep in mind that these alternatives may have slightly different performance characteristics or behavior in specific environments.

Overall, both approaches tested in this benchmark are valid and widely supported. The choice between them usually comes down to personal preference, coding style, or specific requirements of the project.

Related benchmarks:

Typeof x === 'undefined' vs x === undefined (test without syntax error) (version: 0)

Comparing performance of: Typeof check vs Strict equality

Created: 5 years ago by: Guest

Jump to the latest result

Typeof check

Strict equality

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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