get console.timeEnd() to not log all by itself-CodePudding

I would like to get the amount of time the process took to fully complete. I have this code:

console.log(`Ran ${ran} equations in ${console.timeEnd()}`)

but I don't get my expected output, which is:

Ran X equations in 33.099ms // eg

instead I get

default: 33.099ms
Ran X Equations in undefined

Note that I didn't give my console.time() a label.
How can I achieve my expected output?

CodePudding user response：

console.timeEnd doesn't return anything; it's part of the console, as you know. Because console.timeEnd counts in milliseconds with decimal places (unlike Date.now()), the closest thing you'll get is with performance.now(). We can create a custom time function:

class Time {
  constructor() {
    this.time = performance.now();
  }
  end() {
    return (performance.now() - this.time).toFixed(3); // round number to lower decimal precision, like console.time()
  }
}

const time = new Time();
console.time("Console measurement");

let dummyVar = 0;
for(let i = 0; i < 1000000; i  ) {
  // do some time consuming task
  dummyVar  = i;
}

console.log("Custom measurement:", time.end()   "ms");
console.timeEnd("Console measurement");

I intentionally returned a number and not a string (with "ms" at the end) so you could use it better. Obviously, if you want to represent the exact output of console.timeEnd(), simply append "ms" to the expression in Time#end:

class Time {
  constructor() {
    this.time = performance.now();
  }
  end() {
    return (performance.now() - this.time).toFixed(3)   "ms";
  }
}

const time = new Time();

// dummy example
setTimeout(() => console.log(`Ran X equations in ${time.end()}`), Math.floor(Math.random() * 100));

CodePudding user response：

console.timeEnd() returns undefined, not what it logs. To get very close to the desired output, label the timer with the descriptive string...

const ran = 4; // you'll need to know ran before starting the timer
const label = `Ran ${ran} equations in`;
console.time(label);
// do some time consuming stuff
alert('wait a sec, then press ok')
console.timeEnd(label);