Working with Apex I regularly write Javascript. Most of the time these client-side code snippet are blazing fast, but in some cases they take a few seconds to execute.

In these cases I want to see which part of the code is slow. In this process I use two very simple JS functions which make life a lot easier for me:

var timing_start;

function start_timing( text) {
    timing_start = performance.now();
    if ( text) { console.log('Start timing:'+text); } 
}

function show_timing(text)
{ console.log('Timing:'+text+', milliseconds:'+ (performance.now()-timing_start) );  }

You can put this code on the page or include it in a general JS file.

 The use of these functions is really simple:

start_timing();
...
code to be timed 
...
show_timing('Data retrieved');

This will result in the following output in the browser’s console:

Timing:Data retrieved, milliseconds:784.2350000000001

The show timing calls display the elapsed time since the last call to start_timing.

Happy JavaScripting

Source Article from http://dickdral.blogspot.com/2017/04/finding-slow-javascript.html

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