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NodeJ中模块函数/类的实例

multiple-instances ecmascript-5 ecmascript-6 node.js javascript

greengold · 技术社区 · 7 年前

我有一个项目最初是ES5.1,后来我将其更改为支持ES6,所以我使用了async await,let。。。

我找到了 this 帖子解释了过程,但是。。。

当我这样做时:

'use strict';

let _ = require('lodash');
var mappings;

function SafeRequestHandler(reqMappings) {

    if (!(this instanceof SafeRequestHandler)) {
        return new SafeRequestHandler((reqMappings));
    }

    mappings = reqMappings;
}

function safeHandleReq(req, res) {
    try {
        let pair = _.find(mappings, {'url': req.url});
        return pair.handler(req, res);
    } catch (err) {
        console.log(err);
    }
}

SafeRequestHandler.prototype.safe = safeHandleReq;

module.exports = SafeRequestHandler;

但现在,每次我这样做:

var handler = require('../util/safeRequestHandler');

let handlerMappings = [
    {
        url: def.party_create,
        handler: partyCreate
    },
    {
        url: def.party_modify,
        handler: partyModify
    },
    {
        url: def.party_get,
        handler: partyGet
    }
];

var handle = new handler(handlerMappings).safe;

我明白了 this.mappings SafeRequestHandler 这不是一个例子。

所以我尝试了ES6方法来定义处理程序:

'use strict';

let _ = require('lodash');

class SafeRequestHandler {

    constructor(reqMappings) {
        this.mappings = reqMappings;
    }

    safeHandleReq(req, res) {
        try {
            let pair = _.find(this.mappings, {'url': req.url});
            return pair.handler(req, res);
        } catch (err) {
            console.log(err);
        }
    }

}

并将其实例化为:

let handlerMappings = [
    {
        url: def.party_create,
        handler: partyCreate
    },
    {
        url: def.party_modify,
        handler: partyModify
    },
    {
        url: def.party_get,
        handler: partyGet
    }
];

let handle = new SafeRequestHandler(handlerMappings).safeHandleReq;

mappings 在里面 safeHandleReq(...) this 未定义, 映射 未定义

我想我只是没有完全理解基本原理,所以你能纠正一下吗;解释这两种方法有什么问题?

2 回复 | 直到 5 年前

Hitmands 7 年前

如果存储 method 将特定类实例转换为变量。

// handle doesn't have a pointer to its context (aka, this)
let handle = new SafeRequestHandler(handlerMappings).safeHandleReq;
// so handle() will output cannot read property mappings of undefined

const instance = new SafeRequestHandler(handlerMappings);

const handle = (...args) => instance.safeHandleReq(...args);

更多信息请点击此处: Losing "this" context in JavaScript when passing around members

Jonas Wilms 7 年前

价值你可以使用

 let _ = require('lodash');
function SafeRequestHandler(reqMappings) {
  if (!(this instanceof SafeRequestHandler)) {
    return new SafeRequestHandler((reqMappings));
  }
   this.mappings = reqMappings;
}

SafeRequestHandler.prototype.safeHandleReq =  function(req, res) {
    try {
        let pair = _.find(this.mappings, {'url': req.url});
        return pair.handler(req, res);
    } catch (err) {
        console.log(err);
    }
}
module.exports = SafeRequestHandler;