What does ':' do in javascript?

Question

I'm learning javascript and while browsing throught the JQuery library I see ':' being used alot. What is this used for in javascript?

// Return an array of filtered elements (r)
// and the modified expression string (t)
   return { r: r, t: t };

Answer 1

var o = {
    r: 'some value',
    t: 'some other value'
};

is functionally equivalent to

var o = new Object();
o.r = 'some value';
o.t = 'some other value';

Answer 2

That's JSON, or JavaScript Object Notation. It's a quick way of describing an object, or a hash map. The thing before the colon is the property name, and the thing after the colon is its value. So in this example, there's a property "r", whose value is whatever's in the variable r. Same for t.

Answer 3

It is part of the object literal syntax. The basic format is:

var obj = { field_name: "field value", other_field: 42 };

Then you can access these values with:

obj.field_name; // -> "field value"
obj["field_name"]; // -> "field value"

You can even have functions as values, basically giving you the methods of the object:

obj['func'] = function(a) { return 5 + a;};
obj.func(4);  // -> 9

Answer 4

The ':' is a delimiter for key value pairs basically. In your example it is a Javascript Object notation.

In javascript, Objects are defined with the colon delimiting the identifier for the property, and its value so you can have the following:

return { 
    Property1 : 125,
    Property2 : "something",
    Method1 : function() { /* do nothing */ },
    array: [5, 3, 6, 7]
};

and then use it like:

var o =  { 
    property1 : 125,
    property2 : "something",
    method1 : function() { /* do nothing */ },
    array: [5, 3, 6, 7]
};

alert(o.property1); // Will display "125"

It is also known as JSON (Javascript Object Notation) which is useful in AJAX calls because it is compact and quick to parse in server-side languages and Javascript can easily de-serialize a JSON string into an object like:

// The parenthesis '(' & ')' around the object are important here
var o = eval('(' + "{key: \"value\"}" + ')');

You can also put the key inside quotes if it contains some sort of special character or spaces, but I wouldn't recommend that because it just makes things harder to work with.

Answer 5

You guys are forgetting that the colon is also used in the ternary operator (though I don't know if jquery uses it for this purpose).

the ternary operator is an expression form (expressions return a value) of an if/then statement. it's used like this:

var result = (condition) ? (value1) : (value2) ;

A ternary operator could also be used to produce side effects just like if/then, but this is profoundly bad practice.

Answer 6

And also, a colon can be used to label a statement. for example

var i = 100, j = 100;
outerloop:
while(i>0) {
  while(j>0) {
   j++

   if(j>50) {
     break outerloop;
   }
  }
i++

}

Answer 7

Just thought I'd mention that another use of the colon is to assign data types to variables -

var s : String;

means that the variable s is of type String