回调需要两个参数
我在node.js中设计一个简单的Web应用程序,我们只是使用index.js
回调到rectangle.js
模块。但是,我收到此回调错误,并且不明白导致此问题的语法: -
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)
rectangle.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! [email protected] start: `node index`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the [email protected] start script.
npm ERR! This is probably not a problem with npm. There is likely additional log
ging output above.
回答如下:
您需要编辑setTimeOut函数,在上面的代码中将返回值从callback()传递给setTimeout,即不是函数。将两个setTimeout函数更改为此
setTimeout(function() {
callback(
new Error('length and width needs to be greater than zero'),
null,
);
}, 2000);
和其他功能
setTimeout(function() {
callback(null, {
perimeter: () => 2 * (x + y),
area: () => x * y,
});
}, 2000);
现在它有效