Use

The type property specifies the type of the attribute. The type can be specified as either a type function that returns the type coerced value or one of the following strings:

• "string" - Converts the value to a string except null or undefined.
• "date" - Converts the value to a date or null if the date can not be converted.
• "number" - Passes the value through parseFloat except for null or undefined.
• "boolean" - Converts falsey, "false" or "0" to false and everything else to true.
• "htmlbool" - Like boolean, but also converts empty strings to true. Used, for example, when input is from component attributes like <can-tabs reverse/>
• "compute" - If the value set is a compute, will allow the returning of the computed value.
• "*" - Prevents the default type coersion of converting Objects to Maps and Arrays to Lists.

Basic Example

The following example converts the count property to a number and the items property to an array:

 define: {
   count: {type: "number"},
   items: {
     type: function(newValue){
       if(typeof newValue === "string") {
         return newValue.split(",")
       } else if( Array.isArray(newValue) ) {
         return newValue;
       }
     }
   }
 }

When a user tries to set those properties like:

map.attr({count: "4", items: "1,2,3"});

The number converter will be used to turn count into 4, and the items type converter function will be used to turn items into [1,2,3].

Preventing Arrays and Objects from Automatic Conversion

When an array is passed into a Map setter, it is automatically converted into a List. Likewise, objects are converted into Map instances. This behavior can be prevented like the following:

 define: {
   locations: {type: "*"}
 }

When a user tries to set this property, the resulting value will remain an array.

map.attr('locations', [1, 2, 3]); // locations is an array, not a List

Working with the 'compute' type

Setting type as compute allows for resolving a computed property with the .attr() method.

MyMap = Map.extend({
  define: {
    value: {
      type: "compute"
    }
  }
});

var myMap = new MyMap();
var c = compute(5);

myMap.attr("value",c);
myMap.attr("value"); //-> 5

c(6);
myMap.attr("value"); //-> 6

//Be sure if setting to pass the new compute
var c2 = compute("a");
myMap.attr("value",c2);
myMap.attr("value"); //-> "a"