If I have a javascript object that looks like below
var columns = {
left: true,
center : false,
right : false
}
and I have a function that is passed both the object, and a property name like so
//should return false
var side = read_prop(columns, 'right');
what would the body of read_prop(object, property) look like?
This question is related to
javascript
object
You don't need a function for it - simply use the bracket notation:
var side = columns['right'];
This is equal to dot notation, var side = columns.right;, except the fact that right could also come from a variable, function return value, etc., when using bracket notation.
If you NEED a function for it, here it is:
function read_prop(obj, prop) {
return obj[prop];
}
To answer some of the comments below that aren't directly related to the original question, nested objects can be referenced through multiple brackets. If you have a nested object like so:
var foo = { a: 1, b: 2, c: {x: 999, y:998, z: 997}};
you can access property x of c as follows:
var cx = foo['c']['x']
If a property is undefined, an attempt to reference it will return undefined (not null or false):
foo['c']['q'] === null
// returns false
foo['c']['q'] === false
// returns false
foo['c']['q'] === undefined
// returns true
ThiefMaster's answer is 100% correct, although I came across a similar problem where I needed to fetch a property from a nested object (object within an object), so as an alternative to his answer, you can create a recursive solution that will allow you to define a nomenclature to grab any property, regardless of depth:
function fetchFromObject(obj, prop) {
if(typeof obj === 'undefined') {
return false;
}
var _index = prop.indexOf('.')
if(_index > -1) {
return fetchFromObject(obj[prop.substring(0, _index)], prop.substr(_index + 1));
}
return obj[prop];
}
Where your string reference to a given property ressembles property1.property2
Code and comments in JsFiddle.
Since I was helped with my project by the answer above (I asked a duplicate question and was referred here), I am submitting an answer (my test code) for bracket notation when nesting within the var:
<html>_x000D_
<head>_x000D_
<script type="text/javascript">_x000D_
function displayFile(whatOption, whatColor) {_x000D_
var Test01 = {_x000D_
rectangle: {_x000D_
red: "RectangleRedFile",_x000D_
blue: "RectangleBlueFile"_x000D_
},_x000D_
square: {_x000D_
red: "SquareRedFile",_x000D_
blue: "SquareBlueFile"_x000D_
}_x000D_
};_x000D_
var filename = Test01[whatOption][whatColor];_x000D_
alert(filename);_x000D_
}_x000D_
</script>_x000D_
</head>_x000D_
<body>_x000D_
<p onclick="displayFile('rectangle', 'red')">[ Rec Red ]</p>_x000D_
<br/>_x000D_
<p onclick="displayFile('square', 'blue')">[ Sq Blue ]</p>_x000D_
<br/>_x000D_
<p onclick="displayFile('square', 'red')">[ Sq Red ]</p>_x000D_
</body>_x000D_
</html>Source: Stackoverflow.com