Javascript尾递归而不是循环

Question

In one of Douglas Crockford speeches, He favours the use of tail recursion over loops. this code was presented,

function repeat(myFunc) {
  if (myFunc !== undefined) {
    return repeat(myFunc);
  }
}

I thought to define a myFunc but don't know if a static counter can retain its state during function calls or use a global counter. but being new to javascript I wanted to ask first. How can this be used in an example, say to count down from 10 to 0? Thanks.

Answer 1

How can this be used in an example, say to count down from 10 to 0?

Pass a Number to repeat , call repeat with decremented number as parameter until variable parameter is equal to 0

 function repeat(n) { console.log(n) if (n) { return repeat(--n); } } repeat(10) 

Answer 2

You need to call the function myFunc somewhere -- and evaluate the result for further call of repeat .

 function repeat(myFunc) { if (myFunc()) { repeat(myFunc); } } var count = 10; repeat(function () { document.write(count + '<br>'); count--; return count >= 0; }); 

Answer 3

Here is a version that keeps state without global variable:

 function repeat(myFunc, arg) { if ((arg = myFunc(arg)) !== undefined) { repeat(myFunc, arg); } } repeat(function (count) { document.write(count + ','); count--; if (count >= 0) return count; }, 10); 

Answer 4

Not sure if I understand what approach you want, but you can use this to count down recursively

function repeat(myFunc, times) {
  if(times > 0 && typeof myFunc == 'function') {
    myFunc(times);
    repeat(myFunc, times-1);
  }
}
repeat(alert, 10);