Remember what I always advise: always use the JS++ Standard Library if you can. The methods aren’t just well-tested for validity, but we also test for performance.
Checking if a number is even or odd is the classic fizzbuzz test. Most professional developers can use the modulus operator. However, that’s not always the fastest implementation.
> var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i & 1) == 0; console.log(x); new Date - t; false 87 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i & 1) == 0; console.log(x); new Date - t; false 90 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i & 1) == 0; console.log(x); new Date - t; false 86 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i & 1) == 0; console.log(x); new Date - t; false 86 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i & 1) == 0; console.log(x); new Date - t; false 86 = 87ms > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i % 2) == 0; console.log(x); new Date - t; false 105 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i % 2) == 0; console.log(x); new Date - t; false 100 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i % 2) == 0; console.log(x); new Date - t; false 100 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i % 2) == 0; console.log(x); new Date - t; false 104 > var t = new Date(); var x; for (var i = 0; i < 50000000; ++i) x = (i % 2) == 0; console.log(x); new Date - t; false 101 = 102ms Node.js v8.11.1 Linux x64 Core i7-4790k, 32gb RAM
var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i & 1) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 1948 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i & 1) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2072 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i & 1) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2086 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i & 1) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2092 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i & 1) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2102 = 2060ms var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i % 2) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2058 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i % 2) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2082 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i % 2) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2114 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i % 2) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2102 debugger eval code:1:96 var t = new Date(); var x; for (var i = 0; i < 5000000; ++i) x = (i % 2) == 0; console.log(x); console.log(new Date - t); false debugger eval code:1:80 2104 debugger eval code:1:96 = 2092ms Firefox 59.0.2, Linux x64 Core i7-4790k, 32gb RAM
While the results are not statistically significant in Firefox (because it's very possible SpiderMonkey is manually optimizing this case via a pattern-matched optimization), you can get a 17% performance gain in Node.js via bitwise AND.
Due to all the layers of abstraction in JavaScript, it's not entirely evident how much faster a bitwise AND for isEven/isOdd can really be. In our benchmarks, we were able to achieve a 17% performance improvement in Node.js. As our lead engineer pointed out via email, according to this table, "for Intel Skylake-X `div` has a latency of 26 (for 32-bit integers), whereas `and` has latency 1 ("reciprocal throughput" has similar difference) so it is an order of magnitude slower, not 20% as in your tests."
Look for isEven() and isOdd() to appear in a future version of the JS++ Standard Library.
You may also be interested in reading Part II of this post which describes how we leveraged overflow behavior to improve performance while preserving correctness for UInteger32.
Roger Poon