variable in javascript statement - javascript

How does one add a variable string in this javascript statement?
where name may correspond to any valid string , say WebkitTransform or Moztransform,etc
document.getElementById('test').style.VARIABLE_NAME = 'rotate(15deg)';
My code doesn't seem to work when i set the VARIABLE_NAME to WebkitTransform, but it works fine if I use WebkitTransform directly, as in without naming it via a variable.
Thanks in advance :)

There are two ways to access members of a Javascript object.
Dot notation, which uses an identifier to access the member:
obj.member;
Bracket notation, which uses a string to access the member:
obj['member']
The latter uses a string to locate the member and you can just as easily use any expression. The value of the expression will be converted to a string so these are equivalent:
obj[{}]
obj['[object Object]']
If your expression is already a string it will be used as is, and in your case your variable holds a string so you can just do:
document.getElementById('test').style[VARIABLE_NAME] = 'rotate(15deg)';

There are 2 ways of accessing values in javascript objects. The first one is by using the dot operator(e.g. object.memberName). The second one is by using the square bracket notation(e.g. object['memberName']).

Related

node js not accepting hyphen in json [duplicate]

I am using this script to make a style object of all the inherited, etc. styles.
var style = css($(this));
alert (style.width);
alert (style.text-align);
With the following, the first alert will work fine, but the second one doesn't... it's interpreting the - as a minus I assume. The debugger says 'uncaught reference error'. I can't put quotes around it, though, because it isn't a string. So how do I use this object property?
Look at the comments. You will see that for CSS properties, the key notation is not compatible with a number of properties. Using the camel case key notation therefore is the current way:
obj.style-attr // would become
obj["styleAttr"]
Use key notation rather than dot
style["text-align"]
All arrays in JavaScript are objects and all objects are just associative arrays. This means you can refer to a place in an object just as you would refer to a key in an array.
arr[0]
or the object
obj["method"] == obj.method
A couple things to remember when accessing properties this way:
they are evaluated so use strings unless you are doing something with a counter or using dynamic method names.
This means obj[method] would give you an undefined error while obj["method"] would not
You must use this notation if you are using characters that are not allowed in JavaScript variables.
This regex pretty much sums it up:
[a-zA-Z_$][0-9a-zA-Z_$]*
The answer to the original question is: place the property name in quotes and use array style indexing:
obj['property-with-hyphens'];
Several have pointed out that the property you are interested in is a CSS property. CSS properties that have hyphens are automatically converted to camel casing. In that case you must use the camel cased name like:
style.textAlign;
However this solution only works for CSS properties. For example,
obj['a-b'] = 2;
alert(obj.aB); // undefined
alert(obj['a-b']); // 2
CSS properties with a - are represented in camelCase in JavaScript objects. That would be:
alert( style.textAlign );
You could also use a bracket notation to use the string:
alert( style['text-align'] );
Property names may only contain characters, numbers, the well known $ sign and the _ (thanks to pimvdb).
Use brackets:
var notTheFlippingStyleObject = {
'a-b': 1
};
console.log(notTheFlippingStyleObject["a-b"] === 1); // true
More information on objects: MDN
NOTE: If you are accessing the style object, CSSStyleDeclaration, you must use camelCase to access it from JavaScript. More information is here.
alert(style.textAlign)
or
alert(style["textAlign"]);
To directly answer the question: style['text-align'] is how you would reference a property with a hyphen in it. But style.textAlign (or style['textAlign']) is what should be used in this case.
Hyphenated style properties are referenced via camelCase in JavaScript, so use style.textAlign.
To solve your problem: The CSS properties with hyphens in them are represented by JavaScript properties in camelCase to avoid this problem. You want: style.textAlign.
To answer the question: Use square bracket notation: obj.prop is the same as obj["prop"] so you can access property names using strings and use characters that are forbidden in identifiers.
I think in the case of CSS styles they get changed to camelCase in JavaScript, so test-align becomes textAlign.
In the general case, where you want to access a property that contains non-standard characters, you use array-style: ['text-align']
The object property names are not one-to-one matches for the CSS names.
At first, I wondered why the solution didn't work on my end:
api['data-sitekey'] // Returns undefined
...later on I figured out that accessing data attributes was different:
It should be like this:
var api = document.getElementById("some-api");
api.dataset.sitekey

why we need to use [ ] for access variable name include hyphan?

Either if you saying '-' takes as a subtract expression.
eg. Json = {'Me-m':123}
But have you idea why we need to use [] for access this hyphen variable.
Such like that Json['Me-m'].
Writting
Json.Me-m
will evaluate to
Json.Me - m
It will try to access Me property from Json object and subtract m variable, which probably will be undefined.
Because Me-m is not a valid property name to be used as property hence you are forced to use as Maps read this or check here for a valid propert name
That's because '-' has a meaning in javaScript, so if you write Json.Me-m JavaScript interprets: 'Substract the value of the variable m to the value of the attribute Me of the object ``Json`'.
In javascript, you can access any member of an object by name, using [], and inside a string, javascript is not going to try to evaluate anything, so when you write Json[Me-m], it's interpreted as: 'Retrieve the value of the member named Me-m of the object Json'
The reason is simple: in Javascript each object it's an indexed key/value dictionary, accessing to the variable with the "." it's a shortcut, and obviously the fact of the "dictionary object" it's a performance issue, but despite of this matter, javascript it's really fast in comparison with other scripting language.
Answering your question, by desing an index can be a string containing the "-" char, but not a property... so if you have a property with that char, it won't be accessible with the "." notation.
Because you are passing a special character in key part of obj and for accessing that value of obj we need to use [].
eg. json['Me-m']

Significance of javascript function name in quotes in Angularjs

I'm going through a javascript file having some functions like this:
'form_validation': function(form,error_bin){
for(var field in form){
if(field.substr(0,1) != "$"){
this.validation_messages(field,form,error_bin);
}
}
}
I want to understand what is the difference between defining a function with quotes (like mentioned above) and without quotes
EDIT: I've also observed that the functions having name in quotes are being called from a different file (like: ServiceName.functionName()), while without quotes are being called from the same file.
This is an Angularjs code
The two are equivalent syntax for object literals. The quotes allow you to use keys that aren't legal variable names, like so:
var foo ={ 'variable name':2}
There's nothing significant about the fact that the value assigned to the object key is a function. In JavaScript objects are (almost) just key value pairs of strings and arbitrary objects.
JavaScript has something called Objects these are link associative array's in other languages. Object have item. Each item has a key(name) and a value. Key's follow regular JavaScript variable names. You can check valid variable names here. Valid variable names do not need to be in quotes. Sometimes, to include special characters, the name is a string.
my_value <- Valid
my-value <- Invalid (needs to be in string)
my value <- Invalid (needs to be in string)
both are same for javascript objects. but you should avoid using quotes as a coding standard.

Using a dynamically created variable to access named object in an object

finalVariables() returns an object that contains data accessible by .dataName notation i.e. finalVariables().mainViewWindow0 returns the string stored for mainViewWindow0. I'm trying to access mainViewWindow0 using a dynamically created variable, but for obvious reasons this doesn't work so well with dot notation, but I don't know how to work around it. Help to be had for me?
Please ignore the poor coding practice of having a hard-coded number in there; I promise to get rid of it later
activePane = dot.id.substring(6); //gets dot # and sets it as active pane
var tempForPaneNumber = "mainViewWindow" + activePane + "";
document.getElementById("mainViewWindowContent").innerHTML = finalVariables().###this is where I want to use
the string from "tempForPaneNumber" to access ###
finalVariables[tempForPainNumber]()
Should do the trick if I understand correctly.
In Javascript you can access properties of an object either through the dot notation or through the use of brackets to specify the identifier for the property so myVar.foo is equivalent to myVar['foo']. Therefore, if I understand what you are asking correctly you want to use finalVariables()[tempForPaneNumber]()

Create a method from a string in JS

So I have a string "getNumber":
I would like to use this string as a method for an object: myObj.getNumber()
Is that possible?
Thanks
As simple as:
myObj['getNumber']();
There two ways to access value from js object .. one is dot notation . and other is square bracket notation [], which allows access to properties containing special characters and selection of properties using variables.
var key = 'getNumber';
myObj[key]();
More information on Mozilla, working with object guide.

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