Please explain usage of _.identity(value) of underscore.js

Question

Please explain usage of _.identity(value) of underscore.js. Not able to understand it from the documentation ( http://underscorejs.org/#identity ).

Can

Answer 1

A specific example:

Underscore.js defines _.each and as like this.

_.each = function(obj, iterator, context) {
  ...
}

This iterator shows el value. You maybe have used this idiom.

_.each([1, 2, 3], function(el){
  console.log(el);
});

This iterator returns el value without change.

_.each([1, 2, 3], function(el){
  return el;
});

The function that returns a value without change occur frequently. So Underscore.js wants to define the function. Underscore.js names the function _.identity.

_.identity = function(value) {
  return value;
};

If Underscore.js wants to use a default iterator, all Underscore.js need is call _.identity.

_.each([1, 2, 3], _.identity);