Web crawler - node.js crawler External call function cannot obtain variable value

Question

Recently I wanted to write a crawler novel to read, but I encountered some difficulties

console.log(catalogUrl) can print out the required URL

But what I expect is that when I call the function var xxx = getCatalogUrl(book) externally, I can get the value of the catalogUrl variable.
I tried return and global variables, but none of them work.

Help all the experts!

Answer 1

You need to understand js callback promise async/await

//简单的回调例子

asyncFunction(callback);

function callback(data){
    console.log(data)
}

function asyncFunction(cb){
    setTimeout(function(){
        cb && cb(1); //传递一个1出去
    },300);
}

Answer 2

catalogUrl is in the asynchronous function! How to solve the asynchronous problem, look at these materials or Baidu, they are all basic things