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hasDeepProperty in Node JS & JavaScript [duplicate]

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JS checking deep object property existence [duplicate]
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Closed 6 years ago.
After spending many hours today searching for a specific condition functionality and testing my modified finds. I thought I share my coding snippets and knowledge here. I'm not too good at answering other questions so I thought it would do to post my finds and hope it would benefit others. Since this site has been really helpful with my projects.
Anyway. At some point when you get to a stage scripting more complicated scripts. You'll most likely bump into a problem were you'll need to check deep in objects if a certain property exists. This has occurred mostly with JSON API from my experience.
Example Issue
if (someObject && someObject.nextObject && someObject.nextObject.andAnother) {
// do something if all of this exists
}
Trying to check the deepest property, when one property in the middle doesn't exist, will throw a reference error.
ReferenceError: something is not defined
At some point these can get really long and messy to work with. Which is pretty much silly.
Trying to Tidy Like That Makes JSLint Complain & Can Be Harder for Another Scripter to Read
JSLint doesn't like when code ends up like this when scripters try to reduce the amount of characters on one line. Even I find it more difficult to read with other nested conditions together:
if (someObject
&& someObject.nextObject
&& someObject.nextObject.andAnother) {
// do something if all of this exists
}

There's multiple ways of making this less clutter. Below is an example of some different versions of snippet functions for this object.
var object = {
nextObject: {
anArray: [{
value: true
}]
}
};
Boolean Function with String Perimeter
var hasDeepProperty = function (obj, pathString) {
var i, properties = pathString.split("."), l = properties.length;
for (i = 0; i < l; i++) {
if (obj.hasOwnProperty(properties[i])) {
obj = obj[properties[i]];
} else {
return false;
}
}
return true;
};
console.log(hasDeepProperty(object, "nextObject.0.value")); // returns true
console.log(hasDeepProperty(object, "nextObject.doesNotExist.value")); // returns false
Boolean Function with Array Perimeter
var hasDeepProperty = function (obj, pathArray) {
var i, properties = pathArray, l = properties.length;
for (i = 0; i < l; i++) {
if (obj.hasOwnProperty(properties[i])) {
obj = obj[properties[i]];
} else {
return false;
}
}
return true;
};
console.log(hasDeepProperty(object, ["nextObject", 0, "value"])); // returns true
console.log(hasDeepProperty(object, ["nextObject", "doesNotExist", "value"])); // returns false
Prototype Boolean Function with String Perimeter
Object.prototype.hasDeepProperty = function (pathString) {
var i, properties = new String(pathString).split("."), l = properties.length, obj = new Object(this);
for (i = 0; i < l; i++) {
if (obj.hasOwnProperty(properties[i])) {
obj = obj[properties[i]];
} else {
return false;
}
}
return true;
};
console.log(object.hasDeepProperty("nextObject.0.value")); // returns true
console.log(object.hasDeepProperty("nextObject.doesNotExist.value")); // returns false
Prototype Boolean Function with Array Perimeter
Object.prototype.hasDeepProperty = function (pathArray) {
var i, properties = pathArray, l = properties.length, obj = new Object(this);
for (i = 0; i < l; i++) {
if (obj.hasOwnProperty(properties[i])) {
obj = obj[properties[i]];
} else {
return false;
}
}
return true;
};
console.log(object.hasDeepProperty(["nextObject", 0, "value"])); // returns true
console.log(object.hasDeepProperty(["nextObject", "doesNotExist", "value"])); // returns false
I'm aware that declaring with the new keyword that isn't a function simulated as a class is discouraged. But for some reason Prototype causes slice method not to exist for string and same for hasOwnProperty for the object.
I hope others find this useful and there be something like this to be added on the next version of JavaScript.
This my first: post my own QnA. And Happy New Year everyone.

how to check the presence of the element in the array?

please help solve the problem.
live example is here: https://jsfiddle.net/oqc5Lw73/
i generate several tank objects:
var Tank = function(id) {
this.id = id;
Tank.tanks.push(this);
}
Tank.tanks = [];
for (var i = 0; i < 3; i++) {
new Tank(i);
}
Tank.tanks.forEach(function(tank, i, arr) {
console.log(tank);
});
console.log('summary tanks: ' + Tank.tanks.length);
after i delete tank with random index:
var tankDel = Math.floor(Math.random() * (3));
Tank.tanks.splice(tankDel, 1);
Tank.count -= 1;
Tank.tanks.forEach(function(tank, i, arr) {
console.log(tank);
});
console.log('summary tanks: ' + Tank.tanks.length);
i try check tanks massive. if tanks massive contain tank with property 'id' = 0 then i need display alert('tank with id 0 is dead').
but console output follow error message:
Uncaught SyntaxError: Illegal break statement

break is to break out of a loop like for, while, switch etc which you don't have here, you need to use return to break the execution flow of the current function and return to the caller. See similar post here: illegal use of break statement; javascript
Tank.tanks.forEach(function(tank, i, arr) {
if(tank.id == 0) {
tank0Dead = false;
return;
};
});
if(tank0Dead == true) {
alert('tank with id 0 is dead');
};
jsfiddle : https://jsfiddle.net/oqc5Lw73/6/

You can't quit from forEach using break. Just remove break, and it will work.
P.S: honestly, it is better to refactor that code:)

Your only problem is that you can't use the break; statement in a forEach function.
But you can in a for() loop, so here is the equivalent code with a for :
for (var i = 0; i < Tank.tanks.length; i++){
if (Tank.tanks[i].id == 0){
tank0Dead = false;
break;
}
}
https://jsfiddle.net/oqc5Lw73/5/
But I agree with #dimko1 about the idea of refactoring the code

You can not break a forEach callback, simply because it's a function.
Here's updated working jSfiddle
If you really want to break it, you can use exception like code below.
try {
[1,2,3].forEach(function () {
if(conditionMet) {
throw Error("breaking forEach");
}
});
} catch(e) {
}
Otherwise you can use jQuery's each() method. when it's callback returns false it stops.
jQuery.each([1,2,3], function () {
if(conditionMet) {
return false;
}
});

Accessing the value of an observable inside a plain JS array in Knockout JS?

Background
I have a plain JS array, initially empty. I later populate it with values. The values sent to it are numbers that are Knockout observables. Later, I want to compare those values to values in another, knockout observable array. My problem is that whenever I pass the index of the current item in my array loop, and pass that index value (a number!), the array returns a function. To get an idea, look at the JS that follows.
Note that my project and actual script is viewable on JSBin. Further, to view the problem in the console, you have to add assignments, then press 'sort'.
JSBin: http://jsbin.com/fehoq/177/edit]1
JS
//example script that follows actual script
var _this = this;
//initialize my array
this. lowest = [];
// I want to compare values in lowest to values in this array
this.scores = ko.observableArray();
// method that does comparison
this.myMethod = function(){
// initialize my helper, k
var k;
...
// loop through one array
ko.utils.arrayForEach(_this.scores(), function (score) {
// make sure my value is a number...
if (!isNaN(parseFloat(score()))) {
// this is important, I need to current index for comparison
k = _this.scores.indexOf(score);
console.log(k);
// this is where things break - it prints a function, not a value!
console.log(_this.lowest[k]);
// useless check, the value is a function, so they're always different
if (score()!=_this.lowest[k]){
// do stuff
}
}
}
}
Update
Putting the method I'm using, maybe someone will notice something I missed given that my syntax is correct(?).
this.mean = (function(scores,i) {
var m = 0;
var count = 0;
var k;
ko.utils.arrayForEach(_this.scores(), function(score) {
console.log([typeof score(), score()]);
if (!isNaN(parseFloat(score()))) {
console.log(i);
console.log(_this.lowest[i]);
if (score() != _this.lowest[i]) {
m += parseFloat(score());
count += 1;
}
}
});
if (count) {
m = m / count;
return m.toFixed(2);
} else {
return 'N/A';
}
});
}
Update 2
Just in case someone else wanders over here since my problem isn't solve still. The following code is how I set the value of lowest:
this.dropLowestScores = function() {
ko.utils.arrayForEach(_this.students(), function(student){
var comparator = function(a,b){
if(a()<b()){
return 1;
} else if(a() > b()){
return -1;
} else {
return 0;
}
};
var tmp = student.scores().slice(0);
tmp.sort(comparator);
student.lowest = ko.observableArray(tmp.splice((tmp.length-2),tmp.length-1));
});
};
Outstanding Questions, 5/9/2014
Jeremy's script runs but without the desired effects. For example, console.log(_this.lowest[k]) prints undefined, just as mine does. Further, the matched scores aren't skipped, which they should be.
Jeremy's script specifies lowest as a ko.observable. My script also now has lowest as a ko.observable, but why shouldn't a plain JS array work for this? I only need lowest to update when the button it's bound to is clicked, and those bindings are already taken care of.

That is how observables work in Knockout.
When you create one, you are creating a function.
var myObservable1 = ko.observable(); // Create it.
var myObservable2 = ko.observable("Hola!"); // Create it with a value.
console.log(typeof myObservable2); // It is indeed a function
console.log(typeof myObservable2()); // That returns a string
console.log(myObservable2()); // And get the value.
EDIT BASED ON QUESTION IN COMMENTS
var koTest = ko.observableArray();
koTest.push("Line0");
koTest.push("Line1");
koTest.push("Line2");
koTest.push("Line3");
koTest.push("Line4");
var jsTest = [];
jsTest.push("Line0");
jsTest.push("Line1");
jsTest.push("Line2");
jsTest.push("Line3");
jsTest.push("Line4");
alert(koTest()[2]);
alert(jsTest[2]);
alert(koTest()[2] === jsTest[2]);
Test Code
I went ahead and make a runnable test of your code and everything was working just fine for me. I had to make some assumptions about the contents of _this -- in particular the declaration of lowest, which I made an observableArray based on how you were accessing it.
Anyways, this code runs:
var _this = {
scores: ko.observableArray(),
lowest: ko.observableArray()
};
var mean = (function(scores) {
var m = 0;
var count = 0;
var k;
ko.utils.arrayForEach(_this.scores(), function(score) {
console.log([typeof score(), score()]);
if (!isNaN(parseFloat(score()))) {
k = _this.scores.indexOf(score);
console.log(k);
console.log(_this.lowest[k]);
if (score() != _this.lowest[k]) {
m += parseFloat(score());
count += 1;
}
}
});
if (count) {
m = m / count;
return m.toFixed(2);
} else {
return 'N/A';
}
});
for (var i = 0; i < 10; i++) {
_this.scores.push(ko.observable(i));
}
var m = mean();
alert(m);

How to convert javascript array to function

I have an array of arbitrary values. I Wrote a function that transforms the array to an array of functions that return the original values, so instead of calling a[3], I will call a3.
Here is my code which does not work? code. It gives this error Cannot call method '1' of undefined.
var numToFun = [1, 2, { foo: "bar" }];
var numToFunLength = numToFun.length;
function transform(numTo) {
for (var i = 0; i < numToFunLength; i++) {
(function(num){
numTo.unshift(function() {
return num;
});
}(numTo.pop()))
}
}
var b = transform(numToFun);
console.log(numToFun);
console.log(b[1]());​

Others have already answered your question while I was writing mine but I will post it anyway - this may be somewhat easier to follow without all of those popping and unshifting:
function transform(numTo) {
var r = [];
for (var i = 0; i < numTo.length; i++) {
r[i] = (function (v) {
return function() {
return v;
}
}(numTo[i]));
}
return r;
}
(I have also changed the hard-coded length from numToFunLength to numTo.length so the transform() function would work for other inputs than only the global numToFun variable.)
See DEMO.
UPDATE: even more elegant way to do it using the Sugar library:
function transform(array) {
return array.map(function (v) {
return function() {
return v;
}
});
}
I like this syntax because it makes it more explicit that you want to map an array of values to an array of functions that return those values.
See DEMO.

Your function transform does not return anything. That is why b is undefined.
return numTo;
jsFiddle Demo
On the other hand, the array will be passed to the function as a reference anyways, so the original array will be changed. It is not a problem if you don't return anything, just omit the var b = transform(numToFun); line and simply write transform(numToFun).

Your transform function isn't returning anything. So b is undefined

Weird Event Listening in ActionScript3

I have a weird quirk in ActionScript. I need to pass the index to a callback function.
Here is my code
for (var i:Number = 0; ((i < arrayQueue.length) && uploading); i++)
{
var lid:ListItemData=ListItemData(arrayQueue[i]);
var localI:Number= new Number(i); // to copy?
var errorCallback:Function = function():void { OnUploadError(localI); };
var progressCallback:Function = function(e:ProgressEvent):void { lid.progress = e; OnUploadProgress(localI); };
var completeCallback:Function = function():void { Alert.show('callback'+localI.toString()); OnUploadComplete(localI); }; // localI == arrayQueue.length - 1 (when called)
Alert.show(localI.toString()); // shows current i as expected
lid.fileRef.addEventListener(Event.COMPLETE, completeCallback);
lid.fileRef.addEventListener(ProgressEvent.PROGRESS, progressCallback);
lid.fileRef.addEventListener(HTTPStatusEvent.HTTP_STATUS, errorCallback);
lid.fileRef.addEventListener(IOErrorEvent.IO_ERROR, errorCallback);
lid.fileRef.addEventListener(SecurityErrorEvent.SECURITY_ERROR, errorCallback);
lid.fileRef.upload(url, 'File');
}
Any idea on how to pass in the index to my callbacks? .upload does not block.

Passing additional parameters for your callbacks is possible via some kind of delegate function or closure. However it is often considered a bad practice. You may use event target property instead to determine your index based on FileReference.
Edit: here is a sample of using closures:
function getTimerClosure(ind : int) : Function {
return function(event : TimerEvent) {
trace(ind);
};
}
for (var i = 0; i < 10; i++) {
var tm : Timer = new Timer(100*i+1, 1);
tm.addEventListener(TimerEvent.TIMER, getTimerClosure(i));
tm.start();
}
This will continuously trace numbers from 0 to 9.
Edit2: here is a sample of creating a delegate based on a function closure:
function timerHandler(event : Event, ...rest) : void {
trace(event, rest);
}
function Delegate(scope : Object, func : Function, ...rest) : Function {
return function(...args) : void {
func.apply(scope, args.concat(rest));
}
}
var tm : Timer = new Timer(1000, 1);
tm.addEventListener(TimerEvent.TIMER, Delegate(this, this.timerHandler, 1, 2, 3));
tm.start();
However this is a bad approach since unsubscribing for such a listener is a hell pain. This in turn will probably cause some memory leakages, which will decrease overall performance of your application. So, use with caution!
Bottom line: if you know how to work with closures, use them - it is a wonderful thing! If you don't care about your application performance in a long perspective, use closures - it's simple!
But if you are unsure about closures, use a more conventional approach. E.g. in your case you could create a Dictionary that matches your FileReference objects to appropriate indices. Something like that:
var frToInd : Dictionary = new Dictionary(false);
// false here wouldn't prevent garbage collection of FileReference objects
for (var i : int = 0; i < 10; i++) {
// blah-blah stuff with `lib` objects
frToInd[lib.fileRef] = i;
// another weird stuff and subscription
}
function eventListener(event : Event) : void {
// in the event listener just look up target in the dictionary
if (frToInd[event.target]) {
var ind : int = frToInd[event.target];
} else {
// Shouldn't happen since all FileReferences should be in
// the Dictionary. But if this happens - it's an error.
}
}
-- Happy coding!

I have a weird quirk in ActionScript
It's not a quirk, it's variable scope. You should read this article: http://help.adobe.com/en_US/ActionScript/3.0_ProgrammingAS3/WS5b3ccc516d4fbf351e63e3d118a9b90204-7f9d.html#WS5b3ccc516d4fbf351e63e3d118a9b90204-7f8c
And you really shouldn't use anonymous, it just makes everything more confusing. You're actually making multiple copies of the same object.
If the arrayQueue is in scope, you can use this code to get the index:
GetArrayIndex(e.currentTarget);
function GetArrayIndex(object:Object):Number
{
for(var i:Number = 0; 0 < arrayQueue.length; i++)
{
if(object === arrayQueue[i])
return i;
}
}
You should consider using an uint for the index.