js函数的递归调用方法

1.最优秀的方式
var sum=(function(){
    'use strict'
    return  function fun(num){
        if(num<=1){
            return 1;
        }else{
            return num+fun(num-1);
        }
    }
})()

console.log(sum(5));//15

var sumAnother=sum;
console.log(sumAnother(5));//15

sum=null;
console.log(sumAnother(5));//15

2，常规方式
function sum(num){
  if(num<=1){
    return 1;
  }else{
    return num+sum(num-1);
  }
}

console.log(sum(5));//15

3，不提倡方式
function sum(num){
  if(num<=1){
    return 1;
  }else{
    return num+arguments.callee(num-1);
  }
}
console.log(sum(5));//15

var sumAnother=sum;
console.log(sumAnother(5));//15

sum=null;
console.log(sumAnother(5));//15
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