I thought my solution is the ugliest...

Good answer, but the formatting needs some work. The variable names should be descriptive, and the return value should get its own line.

this is needed to return the accumulator result after each iteration

Amazing! 👏🏻👏🏻👏🏻

Looks like in addition to 'Best Practice' and 'Clever' solutions I strongly would like to have the button 'OMG' or 'LOL' :). Anyway, appreciate the persistance of the author!

function factor(){
    let result = '';
    if(peek() > '0' && peek() < '9') return number();

calc('9+1') return emtpy string

so, You should write if(peek() > '0' && peek() <= '9').

LOL...

Thank you, you are right.

Your code is not benchmarking anything significant; you perform the same control operation way too many times, and then only perform the thing to test (Array.from vs [...array]) only once. Naturally the result doesn't indicate anything.

Why are you using document.querySelectorAll('a')? Can't you just, you know, use typical arrays? Like:

var v=[];
for(let i=0; i<1e7; i++) v.push(i);
[...v]

Which would show that Array.from is at least twice as slow.

Hello, after listening to your advice,

I have made some tests as follows, but I have not found that Array.from is slower than [...Arr].

console.time("timer")
obj=document.querySelectorAll('a')
for(let i=1;i<9999999;++i){obj[i]=i}
[...obj]
console.timeEnd("timer");
VM299:5 timer: 948.02685546875ms


console.time("timer")
obj=document.querySelectorAll('a')
for(let i=1;i<9999999;++i){obj[i]=i}
Array.from(obj)
console.timeEnd("timer");
VM300:5 timer: 943.575927734375ms

console.time("timer")
obj=document.querySelectorAll('a')
for(let i=1;i<999;++i){obj[i]=i}
[...obj]
console.timeEnd("timer");
VM340:5 timer: 0.406005859375ms

console.time("timer")
obj=document.querySelectorAll('a')
for(let i=1;i<999;++i){obj[i]=i}
Array.from(obj)
console.timeEnd("timer");
VM341:5 timer: 0.410888671875ms

My Configuration

Google chrome
Version 65.0.3325.181 ( official version ) ( 64 bits )

I guess it must have something to do with V8.

Array.from is slow, very slow, so no.

The best practice is [...]

array.from also didn't exist 2 years ago lol