Node.js 中的异常处理

异常处理是指处理应用程序运行时代码中发生的异常的机制。 Node.js 支持多种传播和处理错误的机制。
以下是可用于 Node.js 中的异常处理的不同方法：

• 同步代码中的异常处理：如果同步代码发生错误，则返回错误。
  例子：
  

javascript

// Write Javascript code here
// Define divider as a synchronous function
var divideSync = function(x, y) {
    // if error condition?
    if ( y === 0 ) {
        // "throw" the error safely by returning it
        return new Error("Can't divide by zero")
    }
    else {
        // no error occurred, continue on
        return x/y
    }
}
 
// Divide 9/3
var result = divideSync(9, 3)
// did an error occur?
if ( result instanceof Error ) {
    // handle the error safely
    console.log("9/3=err", result)
}
else {
    // no error occurred, continue on
    console.log("9/3="+result)
}
 
// Divide 9/0
result = divideSync(9, 0)
// did an error occur?
if ( result instanceof Error ) {
    // handle the error safely
    console.log("9/0=err", result)
}
else {
    // no error occurred, continue on
    console.log("9/0="+result)
}

• 输出：
  

• 基于回调（异步）代码中的异常处理：在基于回调的代码中，回调的参数之一是 err。如果发生错误，则 err 是错误，如果没有发生错误，则 err 为空。 err 参数后面可以跟任意数量的其他参数。
  例子：
  

javascript

// Write Javascript code here
var divide = function(x, y, next) {
    // if error condition?
    if ( y === 0 ) {
        // "throw" the error safely by calling the completion callback
        // with the first argument being the error
        next(new Error("Can't divide by zero"))
    }
    else {
        // no error occurred, continue on
        next(null, x/y)
    }
}
 
divide(9, 3, function(err, result){
    // did an error occur?
    if ( err ) {
        // handle the error safely
        console.log("9/3=err", err)
    }
    else {
        // no error occurred, continue on
        console.log("9/3="+result)
    }
})
 
divide(9, 0, function(err, result){
    // did an error occur?
    if ( err ) {
        // handle the error safely
        console.log("9/0=err", err)
    }
    else {
        // no error occurred, continue on
        console.log("9/0="+result)
    }
})

• 输出：
  

• 事件代码中的异常处理：在事件代码中，错误可能发生在任何地方。因此，与其抛出错误，不如触发错误事件。
  例子：
  

javascript

// Write Javascript code here
// Definite our Divider Event Emitter
var events = require("events")
var Divider = function(){
    events.EventEmitter.call(this)
}
require('util').inherits(Divider, events.EventEmitter)
 
// Add the divide function
Divider.prototype.divide = function(x, y){
    // if error condition?
    if ( y === 0 ) {
        // "throw" the error safely by emitting it
        var err = new Error("Can't divide by zero")
        this.emit("error", err)
    }
    else {
        // no error occurred, continue on
        this.emit("divided", x, y, x/y)
    }
 
    // Chain
    return this;
}
 
// Create our divider and listen for errors
var divider = new Divider()
divider.on('error', function(err){
    // handle the error safely
    console.log(err)
})
divider.on('divided', function(x, y, result){
    console.log(x+"/"+y+"="+result)
})
 
// Divide
divider.divide(9, 3).divide(9, 0)

• 输出：