我将如何使用异步函数作为另一个函数的默认参数

Question

我想创建一个函数，如果该参数不存在，将调用另一个函数。

例如：

function getAllFoo(){ 
    // makes a request to an api and returns an array of all foos 
} 

function getNumFoo(foosArray = getAllFoo(), num = 5){ 
    // selects num of foos from foosArray or calls getAllFoos then selects num of them 
} 

Answer 1

尝试用JS无极来包装异步函数，并在相关的函数调用其then()功能：

function getAllFoo() { 
    return new Promise(
    // The resolver function is called with the ability to resolve or 
    // reject the promise 
    function(resolve, reject) { 
     // resolve or reject here, according to your logic 
     var foosArray = ['your', 'array']; 
     resolve(foosArray); 
    } 
) 
}; 

function getNumFoo(num = 5){ 
    getAllFoo().then(function (foosArray) { 
    // selects num of foos from foosArray or calls getAllFoos then selects num of them 
    }); 
} 

Answer 2

function getAllFoo(){ 
    // makes a request to an api and returns an array of all foos 
} 

function getNumFoo(foosArray = getAllFoo(), num = 5){ 
    // Call getAllFoo() when num is not passed to this function 
    if (undefined === num) { 
     getAllFoo(); 
    } 
} 

Answer 3

你想包异步功能在承诺。

function promiseGetNumFoo(num) { 
     return new Promise((resolve, reject) => 
     // If there's an error, reject; otherwise resolve 
     if(err) { 
      num = 5; 
     } else { 
      num = resolve(result); 
    ).then((num) => 
     // your code here 
    )}