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typeof undefined vs === undefined
(version: 0)
Comparing performance of:
typeof t === "undefined" vs t === undefined
Created:
4 years ago
by:
Guest
Jump to the latest result
Script Preparation code:
var t = "not undefined";
Tests:
typeof t === "undefined"
console.log(typeof t === 'undefined')
t === undefined
console.log(t === undefined)
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (2)
Previous results
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Test case name
Result
typeof t === "undefined"
t === undefined
Fastest:
N/A
Slowest:
N/A
Latest run results:
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Autogenerated LLM Summary
(model
llama3.2:3b
, generated one year ago):
Let's dive into the world of JavaScript microbenchmarks on MeasureThat.net. The provided JSON represents two test cases, each with its own benchmark definition. We'll break down what's being tested and explore the different approaches. **Benchmark Definition** The first section defines a benchmark between `typeof undefined` and `=== undefined`. This is an interesting comparison because `typeof` returns a string describing the type of a variable (`"undefined"` in this case), whereas `===` checks for exact equality. In most JavaScript engines, these two values are not equal. **Script Preparation Code** The script preparation code defines a variable `t` with the value `"not undefined"`. This is done to create a scenario where both conditions are true: `typeof t` returns `"undefined"`, and `t === undefined` returns false. **Html Preparation Code** There's no HTML preparation code, so we'll focus on the script-level comparison. **Options compared** The two test cases compare the following options: 1. **`typeof`**: Returns a string describing the type of a variable (`"undefined"` in this case). 2. **`=== undefined`**: Checks for exact equality with `undefined`. **Pros and Cons** * **`typeof`**: + Pros: Generally faster, as it's an optimized operation. + Cons: May not be equal to `undefined` due to type coercion or other quirks. * **`=== undefined`**: + Pros: Provides a clear indication of whether the variable is exactly equal to `undefined`. + Cons: May be slower, as it involves a more complex comparison. In this specific case, since we're comparing `typeof` and `=== undefined`, the difference in performance will likely be negligible. However, if you need to perform more complex type checks or equality comparisons, `=== undefined` might be a better choice. **Library and purpose** There's no library mentioned in the provided code. The tests rely solely on JavaScript's built-in functionality. **Special JS feature or syntax** None are explicitly used or mentioned. However, it's worth noting that `typeof` and `=== undefined` both rely on JavaScript's type coercion rules, which can sometimes lead to unexpected behavior if not considered carefully. **Other alternatives** If you need to compare other values, such as: * **`value == value`**: This is essentially the same as `=== undefined`, but without checking for strict equality. * **`typeof value === 'undefined'`**: This checks if the value is of type `undefined`, which might be useful in certain scenarios. Keep in mind that these alternatives may have different performance characteristics and should be tested accordingly.
Related benchmarks:
Typeof x === 'undefined' vs x === undefined
Typeof x === 'undefined' vs x === undefined (test without syntax error)
if(typeof <var> ===undefined) vs if(<var>)
typeof number vs not typeof undefined vs undefined
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