Related
I am trying to alert a returned value from a function and I get this in the alert:
[object Object]
Here is the JavaScript code:
<script type="text/javascript">
$(function ()
{
var $main = $('#main'),
$1 = $('#1'),
$2 = $('#2');
$2.hide(); // hide div#2 when the page is loaded
$main.click(function ()
{
$1.toggle();
$2.toggle();
});
$('#senddvd').click(function ()
{
alert('hello');
var a=whichIsVisible();
alert(whichIsVisible());
});
function whichIsVisible()
{
if (!$1.is(':hidden')) return $1;
if (!$2.is(':hidden')) return $2;
}
});
</script>
whichIsVisible is the function which I am trying to check on.
As others have noted, this is the default serialisation of an object. But why is it [object Object] and not just [object]?
That is because there are different types of objects in Javascript!
Function objects:
stringify(function (){}) -> [object Function]
Array objects:
stringify([]) -> [object Array]
RegExp objects
stringify(/x/) -> [object RegExp]
Date objects
stringify(new Date) -> [object Date]
… several more …
and Object objects!
stringify({}) -> [object Object]
That's because the constructor function is called Object (with a capital "O"), and the term "object" (with small "o") refers to the structural nature of the thingy.
Usually, when you're talking about "objects" in Javascript, you actually mean "Object objects", and not the other types.
where stringify should look like this:
function stringify (x) {
console.log(Object.prototype.toString.call(x));
}
The default conversion from an object to string is "[object Object]".
As you are dealing with jQuery objects, you might want to do
alert(whichIsVisible()[0].id);
to print the element's ID.
As mentioned in the comments, you should use the tools included in browsers like Firefox or Chrome to introspect objects by doing console.log(whichIsVisible()) instead of alert.
Sidenote: IDs should not start with digits.
[object Object] is the default toString representation of an object in javascript.
If you want to know the properties of your object, just foreach over it like this:
for(var property in obj) {
alert(property + "=" + obj[property]);
}
In your particular case, you are getting a jQuery object. Try doing this instead:
$('#senddvd').click(function ()
{
alert('hello');
var a=whichIsVisible();
alert(whichIsVisible().attr("id"));
});
This should alert the id of the visible element.
You can see value inside [object Object] like this
Alert.alert( JSON.stringify(userDate) );
Try like this
realm.write(() => {
const userFormData = realm.create('User',{
user_email: value.username,
user_password: value.password,
});
});
const userDate = realm.objects('User').filtered('user_email == $0', value.username.toString(), );
Alert.alert( JSON.stringify(userDate) );
reference
https://off.tokyo/blog/react-native-object-object/
Basics
You may not know it but, in JavaScript, whenever we interact with string, number or boolean primitives we enter a hidden world of object shadows and coercion.
string, number, boolean, null, undefined, and symbol.
In JavaScript there are 7 primitive types: undefined, null, boolean, string, number, bigint and symbol. Everything else is an object. The primitive types boolean, string and number can be wrapped by their object counterparts. These objects are instances of the Boolean, String and Number constructors respectively.
typeof true; //"boolean"
typeof new Boolean(true); //"object"
typeof "this is a string"; //"string"
typeof new String("this is a string"); //"object"
typeof 123; //"number"
typeof new Number(123); //"object"
If primitives have no properties, why does "this is a string".length return a value?
Because JavaScript will readily coerce between primitives and objects. In this case the string value is coerced to a string object in order to access the property length. The string object is only used for a fraction of second after which it is sacrificed to the Gods of garbage collection – but in the spirit of the TV discovery shows, we will trap the elusive creature and preserve it for further analysis…
To demonstrate this further consider the following example in which we are adding a new property to String constructor prototype.
String.prototype.sampleProperty = 5;
var str = "this is a string";
str.sampleProperty; // 5
By this means primitives have access to all the properties (including methods) defined by their respective object constructors.
So we saw that primitive types will appropriately coerce to their respective Object counterpart when required.
Analysis of toString() method
Consider the following code
var myObj = {lhs: 3, rhs: 2};
var myFunc = function(){}
var myString = "This is a sample String";
var myNumber = 4;
var myArray = [2, 3, 5];
myObj.toString(); // "[object Object]"
myFunc.toString(); // "function(){}"
myString.toString(); // "This is a sample String"
myNumber.toString(); // "4"
myArray.toString(); // "2,3,5"
As discussed above, what's really happening is when we call toString() method on a primitive type, it has to be coerced into its object counterpart before it can invoke the method.
i.e. myNumber.toString() is equivalent to Number.prototype.toString.call(myNumber) and similarly for other primitive types.
But what if instead of primitive type being passed into toString() method of its corresponding Object constructor function counterpart, we force the primitive type to be passed as parameter onto toString() method of Object function constructor (Object.prototype.toString.call(x))?
Closer look at Object.prototype.toString()
As per the documentation,
When the toString method is called, the following steps are taken:
If the this value is undefined, return "[object Undefined]".
If the this value is null, return "[object Null]".
If this value is none of the above, Let O be the result of calling toObject passing the this value as the argument.
Let class be the value of the [[Class]] internal property of O.
Return the String value that is the result of concatenating the three Strings "[object ", class, and "]".
Understand this from the following example
var myObj = {lhs: 3, rhs: 2};
var myFunc = function(){}
var myString = "This is a sample String";
var myNumber = 4;
var myArray = [2, 3, 5];
var myUndefined = undefined;
var myNull = null;
Object.prototype.toString.call(myObj); // "[object Object]"
Object.prototype.toString.call(myFunc); // "[object Function]"
Object.prototype.toString.call(myString); // "[object String]"
Object.prototype.toString.call(myNumber); // "[object Number]"
Object.prototype.toString.call(myArray); // "[object Array]"
Object.prototype.toString.call(myUndefined); // "[object Undefined]"
Object.prototype.toString.call(myNull); // "[object Null]"
References:
https://es5.github.io/x15.2.html#x15.2.4.2
https://es5.github.io/x9.html#x9.9
https://javascriptweblog.wordpress.com/2010/09/27/the-secret-life-of-javascript-primitives/
It's the value returned by that object's toString() function.
I understand what you're trying to do, because I answered your question yesterday about determining which div is visible. :)
The whichIsVisible() function returns an actual jQuery object, because I thought that would be more programmatically useful. If you want to use this function for debugging purposes, you can just do something like this:
function whichIsVisible_v2()
{
if (!$1.is(':hidden')) return '#1';
if (!$2.is(':hidden')) return '#2';
}
That said, you really should be using a proper debugger rather than alert() if you're trying to debug a problem. If you're using Firefox, Firebug is excellent. If you're using IE8, Safari, or Chrome, they have built-in debuggers.
[object Object] is the default string representation of a JavaScript Object. It is what you'll get if you run this code:
alert({}); // [object Object]
You can change the default representation by overriding the toString method like so:
var o = {toString: function(){ return "foo" }};
alert(o); // foo
I think the best way out is by using JSON.stringify() and passing your data as param:
alert(JSON.stringify(whichIsVisible()));
You have a javascript object
$1 and $2 are jquery objects, maybe use alert($1.text()); to get text or alert($1.attr('id'); etc...
you have to treat $1 and $2 like jQuery objects.
You are trying to return an object. Because there is no good way to represent an object as a string, the object's .toString() value is automatically set as "[object Object]".
Consider the following example:
const foo = {};
foo[Symbol.toStringTag] = "bar";
console.log("" + foo);
Which outputs
[object bar]
Basically, any object in javascript can define a property with the tag Symbol.toStringTag and override the output.
Behind the scenes construction of a new object in javascript prototypes from some object with a "toString" method. The default object provides this method as a property, and that method internally invokes the tag to determine how to coerce the object to a string. If the tag is present, then it's used, if missing you get "Object".
Should you set Symbol.toStringTag? Maybe. But relying on the string always being [object Object] for "true" objects is not the best idea.
The object whose class is Object seems quite different from the usual class instance object, because it acts like an associative array or list: it can be created by simple object literals (a list of keys and properties), like this: let obj={A:'a',B:'b'}; and because it looks very like this same literal notation when displayed in the Developer Tools Console pane and when it is converted to a JSON string.
But, in fact, the only real difference in objects of other classes (which are derived or extended from Object) is that other classes usually have constructors and methods (these are all functions), in addition to properties (which are variables). A class instance object is allocated using the 'new' operator, and its properties and methods are accessible through the 'this' variable. You can also access the underlying static functions that are copied to each new instance by using the 'prototype' property, and even extend system classes by adding new functions to their prototype object.
The Array object is also derived from Object and is frequently used: it is an ordered, 0-indexed array of variable values.
Object objects, unlike Arrays and other classes are treated simply as associative arrays (sometimes considered ordered, and sometimes considered unordered).
I am trying to alert a returned value from a function and I get this in the alert:
[object Object]
Here is the JavaScript code:
<script type="text/javascript">
$(function ()
{
var $main = $('#main'),
$1 = $('#1'),
$2 = $('#2');
$2.hide(); // hide div#2 when the page is loaded
$main.click(function ()
{
$1.toggle();
$2.toggle();
});
$('#senddvd').click(function ()
{
alert('hello');
var a=whichIsVisible();
alert(whichIsVisible());
});
function whichIsVisible()
{
if (!$1.is(':hidden')) return $1;
if (!$2.is(':hidden')) return $2;
}
});
</script>
whichIsVisible is the function which I am trying to check on.
As others have noted, this is the default serialisation of an object. But why is it [object Object] and not just [object]?
That is because there are different types of objects in Javascript!
Function objects:
stringify(function (){}) -> [object Function]
Array objects:
stringify([]) -> [object Array]
RegExp objects
stringify(/x/) -> [object RegExp]
Date objects
stringify(new Date) -> [object Date]
… several more …
and Object objects!
stringify({}) -> [object Object]
That's because the constructor function is called Object (with a capital "O"), and the term "object" (with small "o") refers to the structural nature of the thingy.
Usually, when you're talking about "objects" in Javascript, you actually mean "Object objects", and not the other types.
where stringify should look like this:
function stringify (x) {
console.log(Object.prototype.toString.call(x));
}
The default conversion from an object to string is "[object Object]".
As you are dealing with jQuery objects, you might want to do
alert(whichIsVisible()[0].id);
to print the element's ID.
As mentioned in the comments, you should use the tools included in browsers like Firefox or Chrome to introspect objects by doing console.log(whichIsVisible()) instead of alert.
Sidenote: IDs should not start with digits.
[object Object] is the default toString representation of an object in javascript.
If you want to know the properties of your object, just foreach over it like this:
for(var property in obj) {
alert(property + "=" + obj[property]);
}
In your particular case, you are getting a jQuery object. Try doing this instead:
$('#senddvd').click(function ()
{
alert('hello');
var a=whichIsVisible();
alert(whichIsVisible().attr("id"));
});
This should alert the id of the visible element.
You can see value inside [object Object] like this
Alert.alert( JSON.stringify(userDate) );
Try like this
realm.write(() => {
const userFormData = realm.create('User',{
user_email: value.username,
user_password: value.password,
});
});
const userDate = realm.objects('User').filtered('user_email == $0', value.username.toString(), );
Alert.alert( JSON.stringify(userDate) );
reference
https://off.tokyo/blog/react-native-object-object/
Basics
You may not know it but, in JavaScript, whenever we interact with string, number or boolean primitives we enter a hidden world of object shadows and coercion.
string, number, boolean, null, undefined, and symbol.
In JavaScript there are 7 primitive types: undefined, null, boolean, string, number, bigint and symbol. Everything else is an object. The primitive types boolean, string and number can be wrapped by their object counterparts. These objects are instances of the Boolean, String and Number constructors respectively.
typeof true; //"boolean"
typeof new Boolean(true); //"object"
typeof "this is a string"; //"string"
typeof new String("this is a string"); //"object"
typeof 123; //"number"
typeof new Number(123); //"object"
If primitives have no properties, why does "this is a string".length return a value?
Because JavaScript will readily coerce between primitives and objects. In this case the string value is coerced to a string object in order to access the property length. The string object is only used for a fraction of second after which it is sacrificed to the Gods of garbage collection – but in the spirit of the TV discovery shows, we will trap the elusive creature and preserve it for further analysis…
To demonstrate this further consider the following example in which we are adding a new property to String constructor prototype.
String.prototype.sampleProperty = 5;
var str = "this is a string";
str.sampleProperty; // 5
By this means primitives have access to all the properties (including methods) defined by their respective object constructors.
So we saw that primitive types will appropriately coerce to their respective Object counterpart when required.
Analysis of toString() method
Consider the following code
var myObj = {lhs: 3, rhs: 2};
var myFunc = function(){}
var myString = "This is a sample String";
var myNumber = 4;
var myArray = [2, 3, 5];
myObj.toString(); // "[object Object]"
myFunc.toString(); // "function(){}"
myString.toString(); // "This is a sample String"
myNumber.toString(); // "4"
myArray.toString(); // "2,3,5"
As discussed above, what's really happening is when we call toString() method on a primitive type, it has to be coerced into its object counterpart before it can invoke the method.
i.e. myNumber.toString() is equivalent to Number.prototype.toString.call(myNumber) and similarly for other primitive types.
But what if instead of primitive type being passed into toString() method of its corresponding Object constructor function counterpart, we force the primitive type to be passed as parameter onto toString() method of Object function constructor (Object.prototype.toString.call(x))?
Closer look at Object.prototype.toString()
As per the documentation,
When the toString method is called, the following steps are taken:
If the this value is undefined, return "[object Undefined]".
If the this value is null, return "[object Null]".
If this value is none of the above, Let O be the result of calling toObject passing the this value as the argument.
Let class be the value of the [[Class]] internal property of O.
Return the String value that is the result of concatenating the three Strings "[object ", class, and "]".
Understand this from the following example
var myObj = {lhs: 3, rhs: 2};
var myFunc = function(){}
var myString = "This is a sample String";
var myNumber = 4;
var myArray = [2, 3, 5];
var myUndefined = undefined;
var myNull = null;
Object.prototype.toString.call(myObj); // "[object Object]"
Object.prototype.toString.call(myFunc); // "[object Function]"
Object.prototype.toString.call(myString); // "[object String]"
Object.prototype.toString.call(myNumber); // "[object Number]"
Object.prototype.toString.call(myArray); // "[object Array]"
Object.prototype.toString.call(myUndefined); // "[object Undefined]"
Object.prototype.toString.call(myNull); // "[object Null]"
References:
https://es5.github.io/x15.2.html#x15.2.4.2
https://es5.github.io/x9.html#x9.9
https://javascriptweblog.wordpress.com/2010/09/27/the-secret-life-of-javascript-primitives/
It's the value returned by that object's toString() function.
I understand what you're trying to do, because I answered your question yesterday about determining which div is visible. :)
The whichIsVisible() function returns an actual jQuery object, because I thought that would be more programmatically useful. If you want to use this function for debugging purposes, you can just do something like this:
function whichIsVisible_v2()
{
if (!$1.is(':hidden')) return '#1';
if (!$2.is(':hidden')) return '#2';
}
That said, you really should be using a proper debugger rather than alert() if you're trying to debug a problem. If you're using Firefox, Firebug is excellent. If you're using IE8, Safari, or Chrome, they have built-in debuggers.
[object Object] is the default string representation of a JavaScript Object. It is what you'll get if you run this code:
alert({}); // [object Object]
You can change the default representation by overriding the toString method like so:
var o = {toString: function(){ return "foo" }};
alert(o); // foo
I think the best way out is by using JSON.stringify() and passing your data as param:
alert(JSON.stringify(whichIsVisible()));
You have a javascript object
$1 and $2 are jquery objects, maybe use alert($1.text()); to get text or alert($1.attr('id'); etc...
you have to treat $1 and $2 like jQuery objects.
You are trying to return an object. Because there is no good way to represent an object as a string, the object's .toString() value is automatically set as "[object Object]".
Consider the following example:
const foo = {};
foo[Symbol.toStringTag] = "bar";
console.log("" + foo);
Which outputs
[object bar]
Basically, any object in javascript can define a property with the tag Symbol.toStringTag and override the output.
Behind the scenes construction of a new object in javascript prototypes from some object with a "toString" method. The default object provides this method as a property, and that method internally invokes the tag to determine how to coerce the object to a string. If the tag is present, then it's used, if missing you get "Object".
Should you set Symbol.toStringTag? Maybe. But relying on the string always being [object Object] for "true" objects is not the best idea.
The object whose class is Object seems quite different from the usual class instance object, because it acts like an associative array or list: it can be created by simple object literals (a list of keys and properties), like this: let obj={A:'a',B:'b'}; and because it looks very like this same literal notation when displayed in the Developer Tools Console pane and when it is converted to a JSON string.
But, in fact, the only real difference in objects of other classes (which are derived or extended from Object) is that other classes usually have constructors and methods (these are all functions), in addition to properties (which are variables). A class instance object is allocated using the 'new' operator, and its properties and methods are accessible through the 'this' variable. You can also access the underlying static functions that are copied to each new instance by using the 'prototype' property, and even extend system classes by adding new functions to their prototype object.
The Array object is also derived from Object and is frequently used: it is an ordered, 0-indexed array of variable values.
Object objects, unlike Arrays and other classes are treated simply as associative arrays (sometimes considered ordered, and sometimes considered unordered).
I understand that when index names are used to push values in Javascript, they essentially work like objects. But what I don't understand is the following behaviour -
person = [];
person[0] = "Someone";
person["test"] = "SomeoneElse"
Inputting person on the console prints ["Someone"] and I could see no information about person.test.
person.test does print SomeoneElse. However, if I go console.log(person), I get ["Someone", test: "SomeoneElse"].
Curious to check if this makes sense, I tried to create a structure like this one -
var experiment = ["Someone1", test1: "SomeoneElse1"]
and what I get is
Uncaught SyntaxError: Unexpected token
What am I missing?
Thanks in advance!
Typing person on the console prints ["Someone"].
Array.prototype.toString formats this output, and it only considers the "array values" of itself without other properties.
However, if I go console.log(person), I get ["Someone", test: "SomeoneElse"].
console.log outputs other information about the object, including own properties.
Uncaught SyntaxError: Unexpected token
Because that is bogus syntax; the array literal syntax doesn't allow keys, because array values aren't supposed to have keys. Arrays are a numerically indexed list of values. Merely by the fact that under the hood those lists are implemented using objects (because everything in Javascript is an object of some kind or another) are you able to set "non numeric keys" on the array. That doesn't mean you're using the array correctly though.
Also see Are JavaScript Array elements nothing more than Array object properties?
This is because an array in JavaScript is also an object itself, and objects can have properties. So it is perfectly valid to have an array with elements, but also have properties set on the array object.
The second example doesn't work because the [...,...,...] syntax is specifically for instantiating an array and its elements.
typing person in console is like having an alert(person); or passing its value to a variable or element, so it is more like you want to get the first set of readable values. That is the reason why it is showing you the values inside, you can try adding person[1] = *something;*, then it will display someone, something
console.log(person) - it displays all the items inside an object. It is more like informing you of what is inside, like a text visualizer in your IDE
var experiment = ["Someone1", test1: "SomeoneElse1"] - it will absolutely throw an exception there is no such format like this on initializing values, at least it is expecting an array format like var experiment = ["Someone1", "SomeoneElse1"]
This works fine:
$cookies.animals = []
$cookies.animals.push({cat: 'meow'})
console.log($cookies.animals) -> [Object]
But identical code inside a factory function doesn't work:
addAnimal: function(id, name, price){
console.log($cookies.animals) //-> [object Object]
$cookies.animals.push({cat: 'meow'}) //-> TypeError: undefined is not a function
}
So why am I getting a TypeError?
If I do this
addAnimal: function(id, name, price){
$cookies.animals = []
console.log($cookies.animals) //-> []
$cookies.animals.push({cat: 'meow'}) //-> works
}
It works (though of course it resets the array) so some something weird is happening to $cookies.animals.
If we look at my console.log inside the factory function:
We get this:
[object Object]
Object with a capital O is my cat, but that weird object is doing something evil I think. Where does it even come from?
Really don't know what's going on to be quite honest. Help please. All I'm trying to do is append to an array...
Per the AngularJS $cookie documentation:
Only a simple Object is exposed and by adding or removing properties to/from this object, new cookies are created/deleted at the end of current $eval. The object's properties can only be strings.
Your initial code works because you can, at any time, set any type of property on any object. Angular does not hold onto your non-string values, though, so your animals property is no longer set in the latter use context. You'll have to serialize and deserialize (probably via JSON) when writing and reading (respectively).
So you'll need to do something like this to initialize the cookie:
var animals = [];
animals.push('Furry Cat');
$cookies.animals = JSON.stringify(animals);
Later when reading, you'd need to do this:
var animal_cookie_value = $cookies.animals,
animals = animal_cookie_value ? JSON.parse(animal_cookie_value) : [];
As for your added remark of:
Object with a capital O is my cat, but that weird object is doing something evil I think. Where does it even come from?
When you see
object Object
in JavaScript you are seeing the output of the default toString() method on JavaScript objects. In other words, you used an object in context of a string, so JS cast it to string (which results in the value you're questioning).
FWIW, I develop a JavaScript cookie library which allows you to pass in any data and it handles the serialization for you. It is currently hosted on Google code, but I am working on moving it to GitHub and hope to add an AngularJS module for it someday.
What is the difference between document.write() method and window.alert() when printing arrays and objects?
The different behaviors are shown in this code sample:
var arr = new Array("Maizere","Pathak");
document.write(arr); // output: Maizere,Pathak
alert(arr); // output: maizere,pathak
Why are they both printing the values? Shouldn't alert() print Object Object?
With a DOM object, it prints [object HTML collection] and here it is printing values.
Objects in JavaScript have a toString method. This method is called whenever the object is used in a way that text is expected. For instance, the following outputs [object Object]:
alert({});
Arrays have their own version of the toString method that does something altogether different. Rather than showing their type, they show their contents, joined by commas. You can replace an arrays toString method if you like:
var names = ['Jonathan', 'Sampson'];
names.toString = function () {
return this.length;
};
alert(names); // Outputs 2
You can use something else's toString implementation too if you like:
document.toString.call(names); // [object Array]
For additional information, see toString on MSDN.
Both alert and document.write are setup to work with the .toString() method. For instances of type object, this usually prints [object Object]. However, the Array class has overloaded this method to print the contents of the array. Try doing arr.toString() to show this is the case. If you create an object and give it a toString method, it will be called for alert. For example:
var obj = {};
obj.toString = function() { return "I'm an Object!"; }
alert(obj);
will show an alert with the string "I'm an Object!" in it.
Both the document.write and window.alert methods use a string, so the Array.toString method will be used to produce a string value from the array.
What the toString method produces from different types of objects may vary between browsers, but you will get the same result from document.write and window.alert as they use the same method to produce the string.
To extend Jonathan Sampson's answer and to give a little mind crusher...
var names = ['Jonathan', 'Sampson'];
names.toString = function () {return 0;};
names.valueOf = function () {return 1;};
console.log(names + ""); // 1 or 0 ? What do you think.
console.log(names.toString()); // 1 or 0 ? What do you think.¨
alert( names );
See demo