Use

The value returned up by a KeyLookup depends on what the key looks like, and what expression type the KeyLookup is within.

For example, {{method(~./key)}} will call method with a compute that looks up the value of key only in the top of the scope.

The rules are as follows:

• Call Expression arguments {{method(key)}} - values are passed.
• Helper Expression arguments {{helper key}} - computes are passed.
• hash value in Call Expression {{method(hash=key)}} - values are set as property values.
• hash value in Helper Expression {{method hash=key}} - computes are set as property values.
• special operator {{%index}} - lookup values in a special context provided by some helpers.
• compute operator {{method(~key)}} - pass a compute instead of a value.
• at operator {{method(@key}} - pass a function instead of trying to read the value of the function.
• current operator {{./key}} - only lookup key at the top of the scope.
• parent operator {{../key}} - lookup the value in the parent context.
• context key {{this}} - return the current context/top of the scope.

Default key return values by expression and data types

Keys can have slightly different default behavior depending if they are used in:

• helper arguments like: {{helper some.key}}

when compared to the other places they are used:

• insertion tags like: {{some.key}}
• call-expression arguments like: {{helper(some.key)}}
• event bindings like: ($click)="method(some.key)"
• data bindings like: {some-attr}="some.key"

Furthermore keys return different values depending on the data type.

In general:

• Functions are called to get their return value. (Use the @ operator to prevent this).
• Keys in helper expression arguments that find observable data return a compute that represents the value.
• Keys in other expressions return the value.
• If no observable data is found, the key’s value is returned in all expressions.

The following illustrates what some.key would return given different data structures as a Helper Expression and in all other expressions.

// A non-observable JS object:
{some: {key: "value"}};
   // Helper -> "value"
   // Other  -> "value"

// A non-observable JS object w/ a function at the end
{some: {key: function(){ return "value"; }}}
   // Helper -> "value"
   // Other  -> "value"

// A non-observable JS object with intermeidate functions:
{some: function(){ return {key: "value"}}}
   // Helper -> "value"
   // Other  -> "value"

// A observable can-map
{some: new Map({key: "value"})}
   // Helper -> canCompute("value")
   // Other  -> "value"

// A method on an observable can-map that reads observables
var Some = Map.extend({key: function(){ return this.attr("value")}})
{some: new Some({value: "value"})}
   // Helper -> canCompute("value")
   // Other  -> "value"