How to measure time taken by a function to execute using JavaScript
Last Updated :
04 Nov, 2025
In JavaScript, you can measure the execution time of a function to analyze performance and optimize code efficiency.
- Use console.time() and console.timeEnd() to measure execution duration.
- Helpful for debugging and identifying performance bottlenecks.
To measure the time taken by a function to execute we have three methods:
[Approach 1]: Using the Using Date Object
We can use the Date object to calculate the time taken by a function. we are using getTime() method from the Date object and then we calculate the average time taking by a function to execute.
HTML
<!DOCTYPE html>
<html>
<head>
<title>Measure Execution Time</title>
</head>
<body>
<h1 style="color: green">GeeksforGeeks</h1>
<b>
How to measure time taken by a function to
execute using JavaScript?
</b>
<p>
Click on the button to measure the time taken by
the function. The output would be displayed on
the console.
</p>
<button onclick="measurePerformance()">
Click to check
</button>
<script type="text/javascript">
function measurePerformance() {
// Get current time in milliseconds
const startTime = new Date().getTime();
exampleFunction();
const endTime = new Date().getTime();
const timeTaken = endTime - startTime;
console.log("Function took " + timeTaken + " milliseconds");
}
function exampleFunction() {
for (let i = 0; i < 1000; i++) {
console.log('Hello Geeks');
}
}
</script>
</body>
</html>
Syntax:
// Get current time in milliseconds
Start = new Date().getTime();
// Your function or code block here
end = new Date().getTime();
// Calculate execution time in milliseconds
executionTime = endTime - startTime;
The Performance.now() method of the performance interface returns a high-resolution timestamp whenever it is called during the program. The time can be measured by getting the starting time before the function and the ending time after the function and then subtracting both of them. This gives the time elapsed for the function.
html
<!DOCTYPE html>
<html>
<head>
<title>Measure Execution Time</title>
</head>
<body>
<h1 style="color: green">
GeeksforGeeks
</h1>
<b>
How to measure time taken by a function
to execute using JavaScript?
</b>
<p>
Click on the button to measure the time
taken by the function. The output would
be displayed on the console.
</p>
<button onclick="measurePerformance()">
Click to check
</button>
<script type="text/javascript">
function measurePerformance() {
start = performance.now();
exampleFunction();
end = performance.now();
timeTaken = end - start;
console.log("Function took " +
timeTaken + " milliseconds");
}
function exampleFunction() {
for (i = 0; i < 1000; i++) {
console.log('Hello Geeks');
}
}
</script>
</body>
</html>
Syntax:
start = performance.now();
function_to_call();
end = performance.now();
[Approach 3]: Using the console.time() method
The Console.time() and timeEnd() methods of the Console object could be used as a timer to measure the time taken between these two methods.
- It takes a label parameter that could be used to distinguish between multiple timers.
- Whenever the timeEnd() method is called, the timer is stopped and the time output is given to the console.
html
<!DOCTYPE html>
<html>
<head>
<title>Measure Execution Time</title>
</head>
<body>
<h1 style="color: green">
GeeksforGeeks
</h1>
<b>
How to measure time taken by a function
to execute using JavaScript?
</b>
<p>
Click on the button to measure the time
taken by the function. The output would
be displayed on the console.
</p>
<button onclick="measurePerformance()">
Click to check
</button>
<script type="text/javascript">
function measurePerformance() {
console.time('function1');
exampleFunction();
console.timeEnd('function1');
}
function exampleFunction() {
for(i= 0;i <1000; i++) {
console.log('Hello Geeks');
}
}
</script>
</body>
</html>
Syntax:
console.time('label');
function_to_call();
console.timeEnd('label');
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