Is there any good example of use cases for angular.identity()?

Question

According to the documentation

A function that returns its first argument. This function is useful when writing code in the functional style.

I am wondering where I can find a good example of such use case - writing code in functional style in an angular app. Thanks

Answer 1

Example from the AngularJS source code:

function transformer(transformationFn, value) {
  return (transformationFn || angular.identity)(value);
};

Explanation:

In case transformationFn is provided as first parameter, it will be called with value as it's own parameter. Otherwise identity function will be called with the same value.

As ng source code mentions:

This function is useful when writing code in the functional style.

What this means is that in functional programming there are no globals, so you always have to pass/inject in everything you need.

Answer 2

Lets say we have these two below functions:

$scope.square = function(n) {
return n * n
};


$scope.multplybyTwo = function(n) {
return n * 2
};

To call this in a functional way:

$scope.givemeResult = function(fn, val) {
return (fn || angular.identity)(val);
};

Then You may use the above function something like below:

$scope.initVal = 5;
$scope.squareResult = $scope.givemeResult($scope.square, $scope.initVal);
$scope.intoTwo = $scope.givemeResult($scope.multplybyTwo, $scope.initVal);

You may follow the below link:

http://litutech.blogspot.in/2014/02/angularidentity-example.html