朋友你听说过尾递归吗

function func(){
    // ... other code
    return otherFunc();// 尾调用
}

function func(){
    // ... other code
    return func();// 尾递归
}

// 实现出来长这样
function fibo(n) {
    if (n <= 0) {
        return 0;
    } else if (n === 1) {
        return 1;
    }
    return fibo(n - 1) + fibo(n - 2)
}

fibo(5)
fibo(4) + fibo(3)
fibo(3) + fibo(2)+  fibo(3)
fibo(2) + fibo(1) + fibo(2)+  fibo(3)
2 + fibo(2) +  fibo(3)
3 + fibo(3)
3 + fibo(2) + fibo(1)
3 + 2
5

function fibo(n, num1 = 1, num2 = 1) {
    if (n <= 0) {
        return 0;
    } else if (n === 1) {
        return num1;
    }
    return fibo4(n - 1, num2, num1 + num2);
}

fibo(5)
fibo(4, 1, 2)
fibo(3, 2, 3)
fibo(2, 3, 5)
fibo(1, 5, 8)

fibo(5);
// 等同于调用
fibo(1, 5, 8);// 中间的调用帧都不需要保存

// 常规递归写法
function fibo(n) {
    if (n <= 0) {
        return 0;
    } else if (n === 1) {
        return 1;
    }
    return fibo(n - 1) + fibo(n - 2)
}

// 常规循环写法
function fibo2(n) {
    if (n <= 0) {
        return 0;
    } else if (n === 1) {
        return 1;
    }
    let x = 0,
        y = 1,
        sum = 0;
    for (let i = 2; i <= n; i++) {
        sum = x + y;
        x = y;
        y = sum;
    }
    return sum;
}

// 公式法
function fibo3(n) {
    if (n <= 0)
        return 0;
    else {
        const sqrtFive = Math.sqrt(5);
        const res = (Math.pow(0.5 + sqrtFive / 2, n) - Math.pow(0.5 - sqrtFive / 2, n)) / sqrtFive;
        return Math.round(res);
    }
}

// 尾递归写法
function fibo4(n, num1 = 1, num2 = 1) {
    if (n <= 0) {
        return 0;
    } else if (n === 1) {
        return num1;
    }
    return fibo4(n - 1, num2, num1 + num2);
}

function test() {
    let tick = Date.now();
    console.log(fibo(50), Date.now() - tick);
    tick = Date.now();
    console.log(fibo2(500), Date.now() - tick);
    tick = Date.now();
    console.log(fibo3(500), Date.now() - tick);
    tick = Date.now();
    console.log(fibo4(500), Date.now() - tick);
    tick = Date.now();
}

// 计算1-N的累加值
function f(n) {
    if (n <= 1) {
        return 1;
    }
    return f(n - 1) + n;
}
f(100000);

// 计算1-N的累加值（尾递归）
function f(n, sum = 1) {
    if (n <= 1) {
        return sum;
    }
    return f(n - 1, sum + n);
}
f(100000);

// 举个例子
function foo(n) {
  return bar(n*2);// 尾调用
}

function bar() {
  throw new Error();
}

foo(1);
// 由于尾调用优化
// 在Error.stack或者开发者工具中，foo的调用帧被丢掉了。

/*
output without PTC
Error
    at bar
    at foo
    at Global Code

output with PTC (note how it appears that bar is called from Global Code)
Error
    at bar
    at Global Code
*/

function factorial(n, acc = 1) {
  if (n === 1) {
    return acc;
  }

  return continue factorial(n - 1, acc * n)
}

#function() { /* all calls in tail position are tail calls */ }

function () { 
    !return expr 
}