javascript - 回调需要两个参数

Question

我正在使用 node.js 设计一个简单的 Web 应用程序，我们只是使用从 index.js 到 rectangle.js 模块的回调。但是，我收到此回调错误，并且不明白哪种语法会导致此错误:-

index.js

// importing rectangle node module
var rect = require('./rectangle')

function solveReact(l, b){
    console.log("l = "+l, "b = ", +b);

// We are using node module to call our callback,
// Note callback, always returns an erorr and function, and takes an error 
// and funciton as parameters
    rect(l, b, (err, rectangle)=> {
        if(err){
            console.log("Error:",err.message);
        }
        else{
            console.log("perimeter:"+ rectangle.perimeter(), "area:"+ 
            rectangle.area());
        }
    });

    // This is after call to react, but this will execute before our rect() 
    //function finishes, because of async calls
    console.log("After rect call")
};

// Some examples
solveReact(5, 6)
solveReact(-2, 3)

矩形.js

// Using node style export
module.exports = (x, y, callback) => {
    if(x <= 0 || y <= 0){
        // simulating a database call error, using delay
        setTimeout(
            callback(new Error("length and width needs to be greater than zero"), 
            null),
            2000);
    }

    else{
        // simulating a successful database call, using delay
        setTimeout(
            callback(null, {
                perimeter: () => (2 * (x + y)),
                area : () => (x*y)
            }),
            2000);
    }
}

错误

l = 5 b =  6
perimeter:22 area:30
timers.js:427
    throw new TypeError('"callback" argument must be a function');
    ^

TypeError: "callback" argument must be a function
    at setTimeout (timers.js:427:11)
    at module.exports (C:\Users\ADMIN\Documents\coursera_server_side_programming
_with_node\simple_node_app\rectangle.js:26:9)
    at solveReact (C:\Users\ADMIN\Documents\coursera_server_side_programming_wit
h_node\simple_node_app\index.js:39:5)
    at Object.<anonymous> (C:\Users\ADMIN\Documents\coursera_server_side_program
ming_with_node\simple_node_app\index.js:54:1)
    at Module._compile (module.js:635:30)
    at Object.Module._extensions..js (module.js:646:10)
    at Module.load (module.js:554:32)
    at tryModuleLoad (module.js:497:12)
    at Function.Module._load (module.js:489:3)
    at Function.Module.runMain (module.js:676:10)
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! simple_node_app@1.0.0 start: `node index`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the simple_node_app@1.0.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional log
ging output above.

Answer 1

您只需调用回调并将该函数调用的结果(不是函数)设置为在setTimeout之后执行。那么为什么你会收到回调参数不是函数的错误。 setTimeout 中的第一个参数的名称名为 callback，这会让您与函数名称混淆 - 错误与此参数有关。您需要在另一个函数中调用您的函数。该函数将在给定时间后调用，届时将调用您的回调

setTimeout(() => callback(new Error("length and width needs to be greater than zero"), null),
           2000);

对代码中的其他 setTimeout-s 执行相同的方法。