问为什么重新分配函数指针会减慢函数调用的速度

EN

function func1() {} // two identical empty functions
function func2() {} // different in name only

var p = func1; // default to func1

var count  = 0; // current loop
var elapse = 0; // elapsed time for 1,000,000 calls on each loop
var start  = 0; // start time for 1,000,000 calls on each loop
var total  = 0; // total elapsed time for all loops

function loop() {

  start = performance.now(); // get start time

  for (let i = 0; i < 1000000; i ++) if (p !== undefined) p(); // do 1,000,000 calls or early out 1,000,000 times if undefined

    elapse = performance.now() - start;

  total += elapse; // used for getting average

  count ++;

  console.log(p + "\nelapsed " + elapse + "\naverage " + total / count);

  // Switch between the lines below to see the performance difference.
  p = (p === func1) ? p = undefined : p = func1; // best performance
  //p = (p === func1) ? p = func1 : p = func1; // good performance
  //p = (p === func1) ? p = func2 : p = func1; // bad performance

  // pattern: func1 -> undefined -> func2 -> undefined -> repeat
  /*if (p === undefined) p = (count % 4 === 0) ? p = func1 : p = func2;
  else p = undefined;*/ // also bad performance

  if (count < 500) loop(); // start the next loop

}

console.clear();

loop(); // start the loop