You have to pass the object you want to iterate, and the JavaScript Object. keys() method will return an array comprising all keys or property names. Then, you can iterate through that array and fetch the value of each property utilizing an array looping method such as the JavaScript forEach() loop.
Since Javascript 1.7 there is an Iterator object, which allows this: 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.
The Object. keys() method was introduced in ES6. It takes the object that you want to iterate over as an argument and returns an array containing all properties names (or keys). You can then use any of the array looping methods, such as forEach(), to iterate through the array and retrieve the value of each property.
What you want is lazy iteration over an object or array. This is not possible in ES5 (thus not possible in node.js). We will get this eventually.
The only solution is finding a node module that extends V8 to implement iterators (and probably generators). I couldn't find any implementation. You can look at the spidermonkey source code and try writing it in C++ as a V8 extension.
You could try the following, however it will also load all the keys into memory
Object.keys(o).forEach(function(key) {
var val = o[key];
logic();
});
However since Object.keys
is a native method it may allow for better optimisation.
Benchmark
As you can see Object.keys is significantly faster. Whether the actual memory storage is more optimum is a different matter.
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);
});
Also remember that you can pass a second argument to the .forEach()
function specifying the object to use as the this
keyword.
// 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);
For simple iteration of key/values, sometimes libraries like underscorejs can be your friend.
const _ = require('underscore');
_.each(a, function (value, key) {
// handle
});
just for reference
I'm new to node.js (about 2 weeks), but I've just created a module that recursively reports to the console the contents of an object. It will list all or search for a specific item and then drill down by a given depth if need be.
Perhaps you can customize this to fit your needs. Keep It Simple! Why complicate?...
'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");
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