var arr = [];
if (!!arr.length) {
console.log(1);
} else {
console.log(0);
}
if (arr.length > 0) {
console.log(1);
} else {
console.log(0);
}
--enable-precise-memory-info
flag.
Test case name | Result |
---|---|
!!array.length | |
array.length > 0 |
Test name | Executions per second |
---|---|
!!array.length | 357896.7 Ops/sec |
array.length > 0 | 344346.7 Ops/sec |
Let's break down the provided benchmark and explain what's being tested, compared, and discussed.
Benchmark Overview
The test measures the performance difference between two approaches to check if an array is not empty:
!!array.length
(also known as the "doublebang" trick)arr.length > 0
Options Compared
Two options are being compared in this benchmark:
a. !!array.length
: This approach uses a double exclamation mark (!!) to force JavaScript to evaluate the expression as a boolean value, even if it's not explicitly marked as such (like if
statements). This is done to avoid issues with some older browsers that might interpret the expression differently.
b. arr.length > 0
: This approach directly checks if the array length is greater than 0 using the comparison operator.
Pros and Cons
a. !!array.length
:
Pros:
- Can work around potential issues in older browsers.
- Often used in practice for concise code.
Cons:
- Less intuitive to read, as it's not immediately clear what it does without knowing the doublebang trick.
- May lead to confusion when debugging.
b. arr.length > 0
:
Pros:
- More straightforward and easy to understand for most readers.
- Avoids potential browser issues by using a standard comparison operator.
Cons:
- May require explicit type checking (in older browsers), which can be slower.
Library and Special JS Feature
In the test case, Yowser
is mentioned in the RawUAString
. Yowser is a feature that allows modern web pages to look like they were designed for mobile devices on desktop computers. It does this by rendering mobile versions of websites as if they were viewed on a mobile device. This feature doesn't affect the performance test itself.
Other Considerations
The benchmark preparation code creates an empty array (var arr = [];
) and defines no variables or functions outside of these lines. The HTML preparation code is null, indicating that no additional setup for the test environment is required beyond what's defined in JavaScript.
For users without deep knowledge of JavaScript:
!!array.length
works by converting a value to a boolean using its truthiness rules.arr.length > 0
directly checks if there are elements in the array, which might be faster on average but relies on explicit type checking.For software engineers who may have worked with JavaScript extensively:
arr.length > 0
) and indirect methods like !!array.length
.