Benchmark: if undefined vs !!

Script Preparation code:

var obj = {};

Tests:

undefined
if(obj.s !== undefined) { var b = 1; }
false
if(!!obj.s) { var b = 1; }

Rendered benchmark preparation results:

Suite status: <idle, ready to run>

Previous results

Test case name	Result
undefined
false

Fastest: N/A

Slowest: N/A

Latest run results:

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

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/111.0.0.0 Safari/537.36

Browser/OS: Chrome 111 on Mac OS X 10.15.7

View result in a separate tab

Test name	Executions per second
undefined	6159799.0 Ops/sec
false	17386148.0 Ops/sec

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

LLMs can make mistakes. Check important info.

Let's dive into the explanation of the provided benchmark.

**What is tested:**
The benchmark measures the performance difference between two approaches:

1. `if (obj.s !== undefined)` (also referred to as "strict inequality" or "identity comparison")
2. `!!obj.s` (also known as "double-bang notation" or "truthy falsy conversion")

**Options being compared:**
The benchmark is comparing the speed of these two approaches for checking if a variable (`obj.s`) is either defined or not.

**Pros and Cons:**

* `if (obj.s !== undefined)`:
	+ Pros:
		- More explicit and readable
		- Avoids potential issues with type coercion
	+ Cons:
		- May be slower due to the comparison operation
* `!!obj.s`:
	+ Pros:
		- More concise and often used in situations where readability isn't a concern
		- Can be faster since it's just a boolean conversion
	+ Cons:
		- Less readable for those unfamiliar with double-bang notation
		- May not work as expected if `obj.s` is an object or array

**Library and purpose:**
There is no explicit library mentioned in the provided benchmark definition. However, the use of `obj.s` suggests that it's a variable defined elsewhere in the script.

**Special JS feature or syntax:**
The double-bang notation (`!!`) is not a built-in JavaScript feature, but rather a common idiom used to convert a value to a boolean. It works by:

* If the value is an object or array, `!!` returns `false`
* Otherwise, it returns `true`

This is because in JavaScript, objects and arrays are considered falsy values when used in a conditional statement.

**Other alternatives:**
If you need to check if a variable is defined, other approaches could be:

1. Using the optional chaining operator (`?.`) (introduced in ES2020):
```javascript
if (obj.s?.length > 0) {
    // ...
}
```
2. Using `typeof` and checking for `"undefined"`:
```javascript
if (typeof obj.s === "undefined") {
    // ...
}
```
3. Using the `in` operator to check if a property exists:
```javascript
if ("s" in obj) {
    // ...
}
```

Keep in mind that these alternatives might have different performance characteristics compared to the original benchmarked approaches.

I hope this explanation helps!

Related benchmarks:

if undefined vs !! (version: 0)

which is faster

Comparing performance of: undefined vs false

Created: one year ago by: Guest

Jump to the latest result

undefined

false

Suite status: <idle, ready to run>

Experimental features:

Fastest: N/A

Slowest: N/A

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