[英]Strange array behaviour in NodeJS
I have the following code written for NodeJS: 我为NodeJS编写了以下代码:
/* server.js */
'use strict';
const http = require('http'),
url = require('url');
METHODS = ['GET','POST','PUT','DELETE'],
_routePathIndex = Array.apply(null, Array(METHODS.length)).map(() => {return []}),
_routeMethodIndex = _routePathIndex.slice(),
_server = http.createServer();
_server.on('request', (req, res) => {
let parsed = url.parse(req.url),
methodIndexVal = METHODS.indexOf(req.method),
PathIndexVal = _routePathIndex[methodIndexVal].indexOf(parsed.pathname);
_routeMethodIndex[methodIndexVal][PathIndexVal](req, res);
});
module.exports = _init();
function _init(){
let rs = { listen: _listen };
METHODS.forEach( (val,i) => {
rs[val.toLowerCase()] = function(route, handler){
_routePathIndex[i].push(route);
_routeMethodIndex[i].push(handler);
};
});
return rs;
};
function _listen(port, callback){
_server.listen(port, callback);
}
To test this out I have the I have a very simple script: 为了进行测试,我有一个非常简单的脚本:
/* server.test.js */
var app = require('./server.js');
app.get('/', (req,res) => { console.log(req, res); });
app.listen(3000, () => { console.log('listening at port', 3000) });
The strangeness begins on line 2 of server.test.js which executes the following code block in server.js, I added the comments to display the values of both _routePathIndex
and _routeMethodIndex
. 奇怪之处始于server.test.js的第2行,该代码在server.js中执行以下代码块,我添加了注释以显示
_routePathIndex
和_routeMethodIndex
的值。
...
rs[val.toLowerCase()] = function(route, handler){
/* _routePathIndex: [ [], [], [], [], ]
_routeMethodIndex: [ [], [], [], [], ] */
_routePathIndex[i].push(route);
/* _routePathIndex: [ ['/'], [], [], [], ]
_routeMethodIndex: [ ['/'], [], [], [], ] */
_routeMethodIndex[i].push(handler);
/* _routePathIndex: [ ['/', [Function]], [], [], [], ]
_routeMethodIndex: [ ['/', [Function]], [], [], [], ] */
};
...
My question is, why is the array acting as tho there are referenced to each other? 我的问题是,为什么作为数组的数组互相引用?
At first, I thought maybe it was the .slice()
that was making the reference but I debunked that by running the following script in the same environment: 最初,我以为可能是
.slice()
构成了引用,但我通过在同一环境中运行以下脚本来揭穿了这一点:
var a = [], b = a.slice();
a.push(1);
console.log(a,b); // [1] [0]
Another thing is when I don't do the .slice()
trick and refactored the code to as such 另一件事是当我不执行
.slice()
技巧并将代码重构为这样的时候
...
_routePathIndex = Array.apply(null, Array(METHODS.length)).map(() => {return []}),
_routeMethodIndex = Array.apply(null, Array(METHODS.length)).map(() => {return []}),
the strange referencing behaviour is gone and the code works Perfect! 奇怪的引用行为消失了,代码可以正常运行!
For added info I'm working with node -v
: v5.4.1
. 有关更多信息,我正在使用
node -v
: v5.4.1
。
Also I tried to clone the array using [].concat(_routePathIndex)
but it still had that weird behaviour 我也尝试使用
[].concat(_routePathIndex)
克隆数组,但它仍然具有怪异的行为
slice
only does a shallow copy, that is _routePathIndex
and _routeMethodIndex
are different, but their elements are the same. slice
仅做一个浅表副本,即_routePathIndex
和_routeMethodIndex
不同,但是它们的元素相同。 Consider this simplified example: 考虑以下简化示例:
a = [[],[]]; b = a.slice(); b[0].push(1); document.write(a)
Get a picture: 获取图片:
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.