var array = new Array(1000);
for (var i = 0; i < array.length; i++) {
array[i];
}
array.forEach(function(i) {
array[i];
});
array.some(function(i) {
array[i];
});
for (var i of array) {
array[i];
}
for (var i = 0, l=array.length; i < l; ++i) {
array[i];
}
--enable-precise-memory-info
flag.
Test case name | Result |
---|---|
for | |
foreach | |
some | |
for..of | |
for cached length |
Test name | Executions per second |
---|---|
for | 125156.8 Ops/sec |
foreach | 986749.8 Ops/sec |
some | 1077035.9 Ops/sec |
for..of | 10113.7 Ops/sec |
for cached length | 289782.5 Ops/sec |
Let's break down the provided benchmark and explain what's being tested, compared, and analyzed.
Benchmark Overview
The benchmark compares the performance of four different loop constructs in JavaScript:
for
loopforEach
method (a part of the Array API)some
method (also a part of the Array API)for..of
loop (introduced in ECMAScript 2015)Loop Constructs
Let's examine each loop construct:
for
loop: A classic, manually managed loop where the index is incremented or decremented.for (var i = 0; i < array.length; i++) {
array[i];
}
Pros: Simple and familiar to many developers. Cons: Manual index management can lead to bugs.
forEach
method: An iterator-based loop that executes a callback function for each element in the array.array.forEach(function(i) {
array[i];
});
Pros: Easy to use, minimal code required. Cons: May not be as efficient as traditional loops, especially for small arrays.
some
method: A short-circuiting loop that returns a boolean value indicating whether at least one element in the array passes a test.array.some(function(i) {
array[i];
});
Pros: Can be useful when only one condition needs to be met. Cons: May not be suitable for all use cases, as it short-circuits.
for..of
loop: A modern, iterator-based loop that executes a block of code for each element in the array.for (var i of array) {
array[i];
}
Pros: Concise and easy to read, with minimal boilerplate code. Cons: May not be as well-supported by older browsers or versions.
Cache-Friendly for
loop
The "cached length" version of the traditional for
loop uses a cached reference to the array's length property:
for (var i = 0, l=array.length; i < l; ++i) {
array[i];
}
Pros: Can be faster for large arrays due to reduced overhead. Cons: Requires manual index management and cache maintenance.
Other Considerations
Alternatives
If you're looking for alternative loop constructs or optimizations, consider:
while
loops: A more flexible option when the number of iterations isn't known.,
Array.prototype.filter(), and
Array.prototype.reduce()` methods: Can be used to perform operations on arrays without manual indexing.Keep in mind that the best loop construct depends on your specific use case, performance requirements, and personal preference.