SOURCE

function de(num) {
    if(num == 1) {
        return 1
    }
    return num + de(num - 1)
}
function add(num) {
    if(num == 1) {
        return 1
    }
    return num * add(num - 1)
}
console.log('xx', add(5))
console.log(de(10))
function getFib(x) {
    if(x==1||x==2){
        return 1
    }
    return getFib(x-1)+getFib(x-2);
}
let a = getFib(3)
console.log(a)
function getChild(arr) {
    if(arr.child.length == 0) {
        return arr.child = []
    }
    return getChild(arr.child)
}