function generateTestArray() { const result = []; for (let i = 0; i < 1000000; ++i) { result.push({ a: i, b: i / 2, r: 0, }); } return result;}const array = generateTestArray();const newMap = new Map();array.forEach((x) => { newMap.set(x.a, x.b);});const foo = [newMap.entries()];const array = generateTestArray();const newMap = new Map();for(const x of array) { newMap.set(x.a, x.b);}const foo = [newMap.entries()];--enable-precise-memory-info flag.
| Test case name | Result |
|---|---|
| .forEach | |
| for..of |
| Test name | Executions per second |
|---|---|
| .forEach | 1.6 Ops/sec |
| for..of | 1.9 Ops/sec |
Let's break down the provided JSON and explain what's being tested, compared, and analyzed.
Benchmark Definition
The benchmark is testing the performance of two JavaScript iteration methods: forEach and for...of. The test creates an array of 1 million objects and measures how long it takes to iterate over this array using each method to add elements to a new Map.
Options Compared
Two options are compared:
.forEach: A traditional loop that iterates over the array using an index, and for each element, calls a callback function with the current element.for...of: A newer loop that iterates directly over the elements of the array, without an index. This allows for more modern and expressive code.Pros and Cons
.forEachPros:
.forEach is supported by all major browsers, including older versions.(x) => { ... }) is easy to read and write.Cons:
for...of: .forEach creates an array of the results, which can be slower for large datasets.for...ofPros:
for...of avoids creating an intermediate result array, making it faster than .forEach.Cons:
for...of.for...of is still less familiar to many developers.Library
There is no explicit library mentioned in the benchmark definition. However, both methods use built-in JavaScript features: Map for storing elements and array iteration.
Special JS Feature or Syntax
The test case uses modern JavaScript syntax, specifically the const keyword with the let declaration. Additionally, it utilizes arrow functions ((x) => { ... }) which are a shorthand way to define small, single-purpose functions.
Other Considerations
.forEach and for...of.Alternatives
Other alternatives for iterating over arrays in JavaScript include:
for loops with an index variable (let i = 0; while (i < array.length) { ... })Array.prototype.reduce(): A method that applies a reduction function to all elements of the array.Array.prototype.forEach() (not used here, but another option for iterating over arrays)Keep in mind that each iteration method has its own strengths and weaknesses, and the choice of which one to use depends on the specific requirements of your project.
