迭代 node.js 中的对象键

Question

从 Javascript 1.7 开始，有一个 Iterator 对象，它允许这样做：

var a={a:1,b:2,c:3};
var it=Iterator(a);

function iterate(){
    try {  
        console.log(it.next());
        setTimeout(iterate,1000);
    }catch (err if err instanceof StopIteration) {  
        console.log("End of record.\n");  
    } catch (err) {  
        console.log("Unknown error: " + err.description + "\n");  
    }  

}
iterate();

node.js 中有这样的东西吗？

我现在正在使用：

function Iterator(o){
    /*var k=[];
    for(var i in o){
        k.push(i);
    }*/
    var k=Object.keys(o);
    return {
        next:function(){
            return k.shift();
        }
    };
}

但是通过将所有对象键存储在k 中会产生大量开销。

Answer 1

您想要的是对对象或数组的惰性迭代。这在 ES5 中是不可能的（因此在 node.js 中是不可能的）。我们最终会得到这个。

唯一的解决方案是找到一个扩展 V8 的节点模块来实现迭代器（可能还有生成器）。我找不到任何实现。您可以查看 spidermonkey 源代码并尝试使用 C++ 将其编写为 V8 扩展。

您可以尝试以下方法，但它也会将所有键加载到内存中

Object.keys(o).forEach(function(key) {
  var val = o[key];
  logic();
});

但是，由于Object.keys 是一种本机方法，它可能会进行更好的优化。

Benchmark

如您所见，Object.keys 明显更快。实际的内存存储是否更优化是另一回事。

var async = {};
async.forEach = function(o, cb) {
  var counter = 0,
    keys = Object.keys(o),
    len = keys.length;
  var next = function() {
    if (counter < len) cb(o[keys[counter++]], next);
  };
  next();
};

async.forEach(obj, function(val, next) {
  // do things
  setTimeout(next, 100);
});

Answer 2

还请记住，您可以将第二个参数传递给.forEach() 函数，指定要用作this 关键字的对象。

// myOjbect is the object you want to iterate.
// Notice the second argument (secondArg) we passed to .forEach.
Object.keys(myObject).forEach(function(element, key, _array) {
  // element is the name of the key.
  // key is just a numerical value for the array
  // _array is the array of all the keys

  // this keyword = secondArg
  this.foo;
  this.bar();
}, secondArg);

Answer 3

调整他的代码：

Object.prototype.each = function(iterateFunc) {
        var counter = 0,
keys = Object.keys(this),
currentKey,
len = keys.length;
        var that = this;
        var next = function() {

            if (counter < len) {
                currentKey = keys[counter++];
                iterateFunc(currentKey, that[currentKey]);

                next();
            } else {
                that = counter = keys = currentKey = len = next = undefined;
            }
        };
        next();
    };

    ({ property1: 'sdsfs', property2: 'chat' }).each(function(key, val) {
        // do things
        console.log(key);
    });

Answer 4

我是 node.js 的新手（大约 2 周），但我刚刚创建了一个模块，它以递归方式向控制台报告对象的内容。它将列出所有项目或搜索特定项目，然后根据需要向下钻取给定的深度。

也许您可以自定义它以满足您的需求。把事情简单化！为什么复杂？...

'use strict';

//console.log("START: AFutils");

// Recusive console output report of an Object
// Use this as AFutils.reportObject(req, "", 1, 3); // To list all items in req object by 3 levels
// Use this as AFutils.reportObject(req, "headers", 1, 10); // To find "headers" item and then list by 10 levels
// yes, I'm OLD School!  I like to see the scope start AND end!!!  :-P
exports.reportObject = function(obj, key, level, deep) 
{
    if (!obj)
    { 
        return;
    }

    var nextLevel = level + 1;

    var keys, typer, prop;
    if(key != "")
    {   // requested field
        keys = key.split(']').join('').split('[');
    }
    else
    {   // do for all
        keys = Object.keys(obj);
    }
    var len = keys.length;
    var add = "";
    for(var j = 1; j < level; j++)
    {
        // I would normally do {add = add.substr(0, level)} of a precreated multi-tab [add] string here, but Sublime keeps replacing with spaces, even with the ["translate_tabs_to_spaces": false] setting!!! (angry)
        add += "\t";
    }

    for (var i = 0; i < len; i++) 
    {
        prop = obj[keys[i]];
        if(!prop)
        {
            // Don't show / waste of space in console window...
            //console.log(add + level + ": UNDEFINED [" + keys[i] + "]");
        }
        else
        {
            typer = typeof(prop);
            if(typer == "function")
            {
                // Don't bother showing fundtion code...
                console.log(add + level + ": [" + keys[i] + "] = {" + typer + "}");
            }
            else
            if(typer == "object")
            {
                console.log(add + level + ": [" + keys[i] + "] = {" + typer + "}");
                if(nextLevel <= deep)
                {
                    // drop the key search mechanism if first level item has been found...
                    this.reportObject(prop, "", nextLevel, deep); // Recurse into
                }
            }
            else
            {
                // Basic report
                console.log(add + level + ": [" + keys[i] + "] = {" + typer + "} = " + prop + ".");
            }
        }
    }
    return ;
};

//console.log("END: AFutils");

Answer 5

对于键/值的简单迭代，有时像 underscorejs 这样的库可以成为您的朋友。

const _ = require('underscore');

_.each(a, function (value, key) {
    // handle
});

仅供参考