Measure performance using console.time

We write several implementation of a computer program, but sometimes confuse about performance and which one to choose. In Javascript, console has a time and timeEnd methods which can be used to measure the execution time of a code block. It starts a timer which you can use to track how long an operation takes.

Example

We have a function which calculates the number of keys in the window object.

So which one will you choose ?

One way

function amISlow() {
	const windowLength = Object.keys(window).length;
	return windowLength;
}

console.time('execution time');
amISlow();
console.timeEnd('execution time');
// execution time: 0.102783203125ms

The other way

const windowLength = Object.keys(window).length;

function amISlow() {
	return windowLength;
}

console.time('execution time');
amISlow();
console.timeEnd('execution time');
// execution time: 0.030029296875ms

You can clearly see that The other way is pretty fast but it does not give any strong reason to use, because, it is polluting the global scope of program. So I shall prefer to go with One way.

But, what if we execute the amISlow several times eg. loop or keypress?

One way

console.time('execution time');
for(let i = 0; i < 100; i+=1) {
	amISlow();
}
console.timeEnd('execution time');
// execution time: 5.300048828125ms

The other way

console.time('execution time');
for(let i = 0; i < 100; i+=1) {
	amISlow();
}
console.timeEnd('execution time');
//execution time: 0.02490234375ms

But, now you can see the performance boost of almost 5ms. You can also justify use of windowLength as a global variable;

I thank Dainel Caldas for detailed discussion and reviewing the post.