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new const vs reassigning let vs reassigning var
(version: 1)
This will evaluate the difference between assigning 2 constants or, creating 1 variable and reassigning it later on.
Comparing performance of:
New consts vs Reassign lets vs Reassign vars
Created:
5 years ago
by:
Registered User
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Tests:
New consts
for(var x = 0; x < 99999999; ++x) { const first = x; const second = x+1; }
Reassign lets
for(var x = 0; x < 99999999; ++x) { let ourLet = x; ourLet = x+1; }
Reassign vars
for(var x = 0; x < 99999999; ++x) { var ourVar = x; ourVar = x+1; }
Rendered benchmark preparation results:
Suite status:
<idle, ready to run>
Run tests (3)
Previous results
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Test case name
Result
New consts
Reassign lets
Reassign vars
Fastest:
N/A
Slowest:
N/A
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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. **Benchmark Definition:** The provided benchmark definition measures the performance difference between three approaches: 1. **Assigning to Constants (`const`)**: This approach assigns values to two constants, `first` and `second`, within a loop. 2. **Reassigning `let` Variables**: In this approach, a variable `ourLet` is declared as `let` and then reassigned the value of itself by adding 1, creating a new value. 3. **Reassigning `var` Variables**: Similarly to the previous approach, but using `var` instead. These approaches differ in how they use variable declarations, which affects performance due to differences in JavaScript's memory management and caching behaviors. **Pros and Cons of Each Approach:** 1. **Assigning to Constants (`const`)**: * Pros: Repeated assignments create a new value each time, reducing the number of updates required. * Cons: It may lead to unnecessary object creation on modern JavaScript engines, potentially causing performance overhead due to garbage collection. 2. **Reassigning `let` Variables**: * Pros: No object creation is involved when reassigning, as it creates a new binding in memory. * Cons: Since `let` variables are scoped and their values are stored on the stack (or heap), reassigning can lead to unnecessary updates of variable bindings. 3. **Reassigning `var` Variables**: * Pros: Similar to reassigning `let`, no object creation is involved. * Cons: Variable declarations using `var` have function scope, which means their values are visible outside the current function, leading to potential pollution and making debugging harder. **Libraries Used (None):** There are no external libraries used in this benchmark definition. **Special JS Features/Syntax (None):** No special JavaScript features or syntax are employed within these test cases. Now that we've broken down the benchmark, let's consider some alternative approaches: * Using `const` for better cache locality and reusing values without object creation. * Implementing a custom compiler to reduce the number of updates required. * Comparing performance with other languages (e.g., C++) or JavaScript engines. * Creating new test cases to explore edge cases. Keep in mind that this benchmark focuses on understanding the performance implications of variable declarations, rather than exploring alternative approaches.
Related benchmarks:
var vs. const vs. let
let vs const in tight loops
var vs const vs let
Reassigning let vs const
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