How to check execution time on every run in JavaScript?

console.time() starts a timer with the name concatenation, which is later stopped by console.timeEnd(). The timer names passed to both function calls have to match in order for the measuring to work.

console.time() and console.timeEnd() are only supported by modern browsers, starting with Chrome 2, Firefox 10, Safari 4, and Internet Explorer 11.

console.time("getFreq");
function getFreq(str){
   var freq={};
  str.replace(/[a-z A-Z]/g, function(match){
  freq[match] = (freq[match] || 0) + 1;
  return match;
  });

 console.log(JSON.stringify(freq));
  return freq;
}
console.timeEnd("getFreq");

• It was executed before doing anything, because the performances test (t0, t1) was outside the method and it was never changed. Put the measurement inside the method.
• I also would check the s to be empty before running the method

function getFreq(str){
  var freq={};
  str.replace(/[a-z A-Z]/g, function(match){
    freq[match] = (freq[match] || 0) + 1;
    return match;
  });
  console.log(JSON.stringify(freq));
  return freq;
}


function doSomething(s){
  if (s === "")
    return;
  var t0 = performance.now();
  getFreq(s);
  var t1 = performance.now();
  console.log("Call to doSomething took " + (t1 - t0) + " ms.")
};

Enter Here : <input type="text" onchange="doSomething(this.value);" />

This is what I want to do for every onChange call

function getFreq(str){
  var t0 = performance.now();
  var freq={};
 str.replace(/[a-z A-Z]/g, function(match){
    freq[match] = (freq[match] || 0) + 1;
    return match;
  });
  console.log(JSON.stringify(freq));
  var t1 = performance.now();
  console.log("Call to doSomething took " + (t1 - t0) + " ms.")
  return freq;
  
}

 <input type="text" onchange="getFreq(this.value);" />

output :

{"a":1,"b":1,"c":3," ":2,"A":1,"D":1}
Call to doSomething took 1.4000000000014552 ms.
{"a":1,"b":1,"c":4," ":3,"A":2,"D":1}
Call to doSomething took 1.9250000000029104 ms.