Benchmark: typeof !== undefined vs strict !equal

Tests:

typeof
var foo = "hello"; typeof foo !== "undefined";
strict equal undefined
var foo = "hello"; foo !== undefined

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
typeof
strict equal undefined

Fastest: N/A

Slowest: N/A

Latest run results:

Run details: (Test run date: 2 years ago)

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/121.0.0.0 Safari/537.36

Browser/OS: Chrome 121 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
typeof	205327936.0 Ops/sec
strict equal undefined	18608850.0 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 benchmark and explain what's being tested.

**Benchmark Overview**

The benchmark is comparing two approaches to check if a variable is not defined or equal to a specific value:

1. `typeof foo !== "undefined"` (using `typeof`)
2. `foo !== undefined` (using strict equality)

**Options Compared**

These are two different ways to express the same idea: checking if a variable is not defined.

* **Option 1:** `typeof foo !== "undefined"` uses the `typeof` operator, which returns a string indicating the type of the variable. If the variable is undefined, `typeof` returns `"undefined"`. This approach is commonly used in JavaScript to check if a variable has been declared.
* **Option 2:** `foo !== undefined` uses strict equality (`!==`) with no quotes around `"undefined"`, which is considered an invalid syntax in most JavaScript implementations. However, some browsers (like Chrome) may still interpret it correctly due to a quirk.

**Pros and Cons of Each Approach**

1. **`typeof foo !== "undefined"`**
	* Pros:
		+ Widespread support across different browsers.
	* Cons:
		+ May be slower than strict equality due to the type conversion.
2. **`foo !== undefined` (invalid syntax)**
	* Pros: None
	* Cons:
		+ Not supported in most JavaScript implementations.
		+ Can lead to unexpected behavior or errors.

**Library and Special JS Feature**

There is no library involved in this benchmark. However, it's worth noting that the `typeof` operator relies on a feature of the JavaScript language called "type checking" or "type inference," which was introduced in ECMAScript 3 (ES3).

**Other Considerations**

When writing JavaScript code, it's essential to consider the nuances of type checking and equality checks. The benchmark highlights an important distinction between `typeof` and strict equality (`!==`). While both approaches can be used to check for undefined values, using `typeof` is generally considered more reliable due to its wider support.

**Alternatives**

If you're interested in exploring alternative ways to check for undefined values or perform type checking, consider the following options:

* Use the `instanceof` operator with a constructor function to check if an object is of a specific type.
* Employ a library like Lodash's `isUndefined()` function or TypeScript's `any` type to simplify type checking.

In summary, the benchmark is testing two approaches to check if a variable is not defined: using `typeof` and strict equality. While both methods have their trade-offs, `typeof` is generally considered more reliable due to its widespread support across browsers.

Related benchmarks:

typeof !== undefined vs strict !equal (version: 0)

Comparing performance of: typeof vs strict equal undefined

Created: 3 years ago by: Guest

Jump to the latest result

typeof

strict equal undefined

Suite status: <idle, ready to run>

Fastest: N/A

Slowest: N/A

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