So, I want to create an object (semi-automatically) using Jquery.
Instead of posting all of my code here, I'll give an example of what I want to do:
var myobject = {
'name1': {
'coord1':true,
'coord2':false,
'coord3':false,
},
'name2': {
'coord4':true,
'coord5':false,
'coord6':false,
}
}
1) I first want to check if 'nameX' is already in my object, if so, continue to step 2, if not, I want to add the name, and coordX with value true or false.
2) If 'nameX' is in the array, I want to check i 'coordX' is in the array. If so, I need to check if the corresponding value (true or false) is the same, and if not, replace it. If 'CoordX' is not in the object, I want to add it with the corresponding value.
For example:
var mynewname = 'name3';
var mynewcoord = 'coord5';
var mynewvalue = 'true';
var mynewname2 = 'name1';
var mynewcoord2 = 'coord4';
var mynewvalue = 'false';
When checking these values with the object this should give:
var myobject = {
'name1': {'
coord1':true,
'coord2':false,
'coord3':false,
'coord4':false
},
'name2': {
'coord4':true,
'coord5':false,
'coord6':false
},
'name3':{
'coord5':true
}
}
I hope someone can help me with this. Thank you
In order to find out if an object contains a property with a given name, you have a couple of choices.
You can use the in operator with a string property name:
if ("nameX" in myobject) {
// The object referenced by `myobject` (or its prototype)
// has its own property called "nameX"
}
else {
// It doesn't
}
in will check the object and its prototype. That probably doesn't matter for the simple objects you're using.
Or you can use hasOwnProperty, which only checks the object and not its prototype:
if (myobject.hasOwnProperty("nameX")) {
// The object referenced by `myobject` has its own property called "nameX"
}
else {
// It doesn't
}
So for instance, if you want to see if name1 is in myobject and, if not, add name1 referencing a blank object, you'd do this:
if (!("name1" in myobject)) {
myobject.name1 = {}; // No, add it and give it a blank object as its value
}
And similarly for the coordX properties of the objects you're referencing from myobject.nameX.
Related
I've got a function to update an object:
_.each(user, function(value, key, obj) {
if (user[key] !== undefined) {
self.user[key] = user[key];
}
});
It lets me update users like this:
let user = new User();
user.verified = true;
self.sessionService.updateSession(user);
I only need to specify properties that are going to be updated by checking for undefined, can this be simplified or written more efficient?
You could do something like this using underscore:
_.assign(self.user, _.omit(user, _.isUndefined))
This works by creating an object where all the keys with undefined values are omitted using omit and the isUndefined predicate.
This object is then used with assign to update the self.user object.
I'm not sure if this is the answer you need, but you can set a variable to new value if it's undefined/null/"" like this:
myVar = myVar || newValue;
If myVar is defined, the old value will be kept. If not, it will be assigned to newValue.
It's difficult to explain the case by words, let me give an example:
var myObj = {
'name': 'Umut',
'age' : 34
};
var prop = 'name';
var value = 'Onur';
myObj[name] = value; // This does not work
eval('myObj.' + name) = value; //Bad coding ;)
How can I set a variable property with variable value in a JavaScript object?
myObj[prop] = value;
That should work. You mixed up the name of the variable and its value. But indexing an object with strings to get at its properties works fine in JavaScript.
myObj.name=value
or
myObj['name']=value (Quotes are required)
Both of these are interchangeable.
Edit: I'm guessing you meant myObj[prop] = value, instead of myObj[name] = value. Second syntax works fine: http://jsfiddle.net/waitinforatrain/dNjvb/1/
You can get the property the same way as you set it.
foo = {
bar: "value"
}
You set the value
foo["bar"] = "baz";
To get the value
foo["bar"]
will return "baz".
You could also create something that would be similar to a value object (vo);
SomeModelClassNameVO.js;
function SomeModelClassNameVO(name,id) {
this.name = name;
this.id = id;
}
Than you can just do;
var someModelClassNameVO = new someModelClassNameVO('name',1);
console.log(someModelClassNameVO.name);
simple as this
myObj.name = value;
When you create an object myObj as you have, think of it more like a dictionary. In this case, it has two keys, name, and age.
You can access these dictionaries in two ways:
Like an array (e.g. myObj[name]); or
Like a property (e.g. myObj.name); do note that some properties are reserved, so the first method is preferred.
You should be able to access it as a property without any problems. However, to access it as an array, you'll need to treat the key like a string.
myObj["name"]
Otherwise, javascript will assume that name is a variable, and since you haven't created a variable called name, it won't be able to access the key you're expecting.
You could do the following:
var currentObj = {
name: 'Umut',
age : 34
};
var newValues = {
name: 'Onur',
}
Option 1:
currentObj = Object.assign(currentObj, newValues);
Option 2:
currentObj = {...currentObj, ...newValues};
Option 3:
Object.keys(newValues).forEach(key => {
currentObj[key] = newValues[key];
});
I have a js object that looks like this:
var object = {
"divisions": {
"ocd-division/country:us": {
"name": "United States",
}
}
};
I want to access the property listed under the nested object "ocd-division/country:us" (aka "name"), but the problem I'm having is that "ocd-division/country" is a variable object. Like it might be ":can" for Canada or something.
My question is, can I still access the name property under that object even though it's variable? I wrote the code I came up with below, but it calls the object literally, so it can't account for a change in the object's name.
var country = document.getElementById("p");
p.innerHTML = object.divisions["ocd-division/country:us"].name;
I'm new to JavaScript so I'm sorry if this is a dumb question.
When you don't know the properties of an object, you can use
for...in loop
It iterates enumerable own and enumerable inherited properties.
Object.keys
It returns an array which contains enumerable own properties.
Object.getOwnPropertyNames
It returns an array which contains own properties.
// Adding properties: "ownEnumerable", "ownNonEnumerable",
// "inheritedEnumerable" and "inheritedNonEnumerable"
var obj = Object.defineProperties({}, {
ownEnumerable: {enumerable: true},
ownNonEnumerable: {},
});
Object.defineProperties(Object.prototype, {
inheritedEnumerable: {enumerable: true},
inheritedNonEnumerable: {},
});
// Display results
function log(id, arr) {
document.getElementById(id).textContent = '[' + arr.join(', ') + ']';
}
log('forin', function(forInProps){
for (var prop in obj) forInProps.push(prop);
return forInProps;
}([]));
log('keys', Object.keys(obj));
log('names', Object.getOwnPropertyNames(obj));
<dl>
<dt><code>for...in</code></dt><dd id="forin"></dd>
<dt><code>Object.keys</code></dt><dd id="keys"></dd>
<dt><code>Object.getOwnPropertyNames</code></dt><dd id="names"></dd>
</dl>
object.divisions[Object.keys(object.divisions)[0]].name
Sure...
for (var division in object.divisions) {
var name = object.divisions[division].name;
// Do what you want with name here
}
If the object has prototype methods you will want to use Object.prototype.hasOwnProperty() to ensure they don't get iterated like so:
for (var division in object.divisions) {
if (!object.divisions.hasOwnProperty(division)) continue;
var name = object.divisions[division].name;
// Do what you want with name here
}
Or use Object.keys() if you don't care about IE8 support and iterate over those.
Object.keys(object.divisions).forEach(function(division) {
var name = object.divisions[division].name;
// Do what you want with name here
});
EDIT: Upon re-reading your question it occurs to me that you may already know the key name but want to access the object with a variable key name, which is also absolutely fine:
var division = 'ocd-division/country:us';
object.divisions[division].name;
When using [] bracket notation to access an object you can insert any code that evaluates to a string, you could even call a function in there that returns a string.
See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Property_Accessors
You can iterate through object using for loop.
var obj = {
"divisions":{
"ocd-division/country:us":{
"name" : "United States"
}
}
}
Here is the for loop
for(var a in obj){ //loop first the object
for(var b in obj[a]){ // then second object (divisions)
for(var c in obj[a][b]){ //then third object (ocd-division/country:us)
if(c == 'name'){ //c is the key of the object which is name
console.log(obj[a][b][c]); //print in console the value of name which is United States.
obj[a][b][c] = "Canada"; //replace the value of name.
var objName = obj[a][b][c]; //or pass it on variable.
}
}
}
}
console.log(obj); //name: Canada
console.log(objName); //name: United States
You can also use this reference:
https://developer.mozilla.org/enUS/docs/Web/JavaScript/Reference/Statements/for
http://stackoverflow.com/questions/8312459/iterate-through-object-properties
I am very new to JS and I was just going through the syntax of modal.js. Basically I have a small difficulty, a lot of classical JS plugins use the below skeleton code for the plugin:
var Modal = function(element , options){
this.options = options
this.$body = $(document.body)
this.$element = $(element)
this.isShown = null
this.$backdrop =
this.scrollbarWidth = 0
}
Modal.prototype.toggle = function (_relatedTarget) {
// do something
}
Modal.prototype.show = function (_relatedTarget) {
// do something
}
var data = new Modal(somthing , radnom);
// now if we assume that option is "show",
//the show function in Modal will be executed
// but my question is data is not an array, so how can we use
// [] square brackets to access the properties of Modal/data ??
data[option](_relatedtarget);
Now my question is about accessing the properties of a plugin, see how a function is being called using the following syntax:
data[option](_relatedtarget);
See my comment in the code. How can we access the properties of data using []; it's not an array, right?
[] are not just for arrays
You can use [] to access properties on an object too.
You can use
data["show"] to access the show method
OR
data.show which is the same thing
One advantage of the [] is that you can use a variable within the brackets
var option = "show";
data[option](something); // call the `show` method on `data`
If you know the method you want to call, using the . is much nicer looking in the code
data.show(something); // much quicker (to type), and prettier
JavaScript has arrays:
var anArray = [ 1, 2, 3, 4 ];
and associative arrays (also known as maps):
var anAssociativeArray = { first: "No. 1", second: 2, somethingElse: "Other" };
both of these data structures can be accessed via []:
anArray[3] // will get the element of the array in position 3
// (starting counting frrom 0).
anAssociativeArray['first'] // will get the element of the associative array with the
// key 'first'.
Associative arrays can also be accessed via the .key notation:
anAssociativeArray.first // will also get the property with key 'first'.
The . notation can be used if you know the key you want to access but if you want to dynamically select which key then you need to use the [] notation.
var whichOptionToPick = 'somethingElse';
var value = anAssociativeArray[ whichOptionToPick ]; // will get the value "Other".
While I realize that an array, as a non-primitive data type, is handled by references in JavaScript, not by value, any particular element of that array could be a primitive data type, and I assume then that it is not assigned by reference.
I'd like to know how to get a reference to an individual element in an array so that I don't have to keep referring to the array and the index number while changing that element?
i.e.
var myElement=someArray[4]
myElement=5
//now someArray[4]=5
Am I misinterpreting various docs that imply but do not explicitly state that this is not the intended behavior?
You can make a copy of an array element, but you can't create a value that serves as an alias for an array property reference. That's also true for object properties; of course, array element references are object property references.
The closest you could get would be to create an object with a setter that used code to update your array. That would look something like:
var someArray = [ ... whatever ... ];
var obj = {
set element5(value) {
someArray[5] = value;
}
};
Then:
obj.element5 = 20;
would update someArray[5]. That is clearly not really an improvement over someArray[5] = 20.
edit — Now, note that if your array element is an object, then making a copy of the element means making a copy of the reference to the object. Thus:
var someArray = [ { foo: "hello world" } ];
var ref = someArray[0];
Then:
ref.foo = "Goodbye, cruel world!";
will update the "foo" property of the object referenced by someArray[0].
You can always pass around a closure to update this:
var myUpdater = function(x) {
someArray[4] = x;
}
myUpdater(5);
If you want read/write capabilities, box it:
var makeBox = function(arr, n) {
return {
read: function() { return arr[n]; },
write: function(x) { arr[n] = x; }
};
}
// and then:
var ptr = makeBox(someArray, 4);
ptr.read(); // original
ptr.write(newValue);
someArray[4]; // newValue