How to find the time taken to execute a function in JavaScript
Overview
We can find the time taken to execute a function by using:
- The
Date.now()object - The
console.timeandconsole.timeEnd() - The
performance.now()function
Using the Date.now() object
We use the Date.now() method to get the current time in milliseconds. The method helps us get the time before and after executing a function. We find the difference between the time after executing the function and the time before executing the function. This will result in the time taken to execute the function.
function test(){
for(let i = 0; i < 1000000000; i++){
}
}
let start = Date.now();
test();
let timeTaken = Date.now() - start;
console.log("Total time taken : " + timeTaken + " milliseconds");Explanation
In the above code,
- Line 1–5: We create a function
testwith aforloop. - Line 6: We get the current time in milliseconds and store in a variable,
start. - Line 7: We call the
testmethod. - Line 8: We calculate the time taken to execute the
testfunction by subtracting the current time from thestarttime, which we will store before executing the function. - Line 9: We print the time taken to execute the
testfunction.
Using console.time and console.timeEnd()
We call the console.time() to initiate a timer with a name. We call the console.timeEnd() to stop the timer. This is used to get the time taken to execute a function.
function test(){
for(let i = 0; i < 1000000000; i++){
}
}
console.time("test_timer");
test();
console.timeEnd("test_timer");Explanation
In the above code:
- Line 1–5: We create a function
testwith aforloop. - Line 6: We call the
console.timemethod withtest_timeras an argument. This will start the timer withtest_timeras the label. - Line 7: We call the
testmethod. - Line 8: We call the
console.timeEndmethod for the labeltest_timer. This will stop the timer and print the number of milliseconds between the call ofconsole.timeandconsole.timeEnd.
Using performace.now
The performance.now method returns the time passed (Read about time origin here). This method returns the time as floating-point numbers with up to microsecond precision.
Explanation
In the above code:
- Line 7–11: We create a function
testwith aforloop. - Line 12: We call the
performance.nowmethod. This will return the elapsed time since the time origin. We store this value in thestartvariable. - Line 13: We call the
testmethod. - Line 14: We call the
performance.nowmethod to get the current elapsed time since the time origin. We subtract this value from the value obtained at the start. This will give the time taken to execute thetestfunction. - Line 15: We print the time taken to execute the
testfunction.
The
performance.nowmethod is the most efficient way to calculate the execution time because we can calculate the execution time with microsecond precision.
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