Added the modifier

lib/model.js

@@ -223,12 +223,17 @@ function compareThings (a, b) {
  * @param {Model} value
  */
 
-// Set a field to a new value
+/**
+ * Set a field to a new value
+ */
 lastStepModifierFunctions.$set = function (obj, field, value) {
   obj[field] = value;
 };
 
-// Push an element to the end of an array field
+
+/**
+ * Push an element to the end of an array field
+ */
 lastStepModifierFunctions.$push = function (obj, field, value) {
   // Create the array if it doesn't exist
   if (!obj.hasOwnProperty(field)) { obj[field] = []; }
@@ -237,9 +242,12 @@ lastStepModifierFunctions.$push = function (obj, field, value) {
   obj[field].push(value);
 };
 
-// Add an element to an array field only if it is not already in it
-// No modification if the element is already in the array
-// Note that it doesn't check whether the original array contains duplicates
+
+/**
+ * Add an element to an array field only if it is not already in it
+ * No modification if the element is already in the array
+ * Note that it doesn't check whether the original array contains duplicates
+ */
 lastStepModifierFunctions.$addToSet = function (obj, field, value) {
   // Create the array if it doesn't exist
   if (!obj.hasOwnProperty(field)) { obj[field] = []; }
@@ -248,7 +256,26 @@ lastStepModifierFunctions.$addToSet = function (obj, field, value) {
   if (obj[field].indexOf(value) === -1) { obj[field].push(value); }
 };
 
-// Increment a numeric field's value
+
+/**
+ * Remove the first or last element of an array
+ */
+lastStepModifierFunctions.$pop = function (obj, field, value) {
+  if (!util.isArray(obj[field])) { throw "Can't $pop an element from non-array values"; }
+  if (typeof value !== 'number') { throw value + " isn't an integer, can't use it with $pop"; }
+  if (value === 0) { return; }
+
+  if (value > 0) {
+    obj[field] = obj[field].slice(0, obj[field].length - 1);
+  } else {
+    obj[field] = obj[field].slice(1);
+  }
+};
+
+
+/**
+ * Increment a numeric field's value
+ */
 lastStepModifierFunctions.$inc = function (obj, field, value) {
   if (typeof value !== 'number') { throw value + " must be a number"; }
 

test/model.test.js

@@ -411,6 +411,49 @@ describe('Model', function () {
 
     });   // End of '$addToSet modifier'
 
+    describe('$pop modifier', function () {
+
+      it('Throw if called on a non array, a non defined field or a non integer', function () {
+        var obj = { arr: 'hello' }
+          , modified;
+
+        (function () {
+          modified = model.modify(obj, { $pop: { arr: 1 } });
+        }).should.throw();
+
+        obj = { bloup: 'nope' };
+        (function () {
+          modified = model.modify(obj, { $pop: { arr: 1 } });
+        }).should.throw();
+
+        obj = { arr: [1, 4, 8] };
+        (function () {
+          modified = model.modify(obj, { $pop: { arr: true } });
+        }).should.throw();
+      });
+
+      it('Can remove the first and last element of an array', function () {
+        var obj
+          , modified;
+
+        obj = { arr: [1, 4, 8] };
+        modified = model.modify(obj, { $pop: { arr: 1 } });
+        assert.deepEqual(modified, { arr: [1, 4] });
+
+        obj = { arr: [1, 4, 8] };
+        modified = model.modify(obj, { $pop: { arr: -1 } });
+        assert.deepEqual(modified, { arr: [4, 8] });
+
+        // Empty arrays are not changed
+        obj = { arr: [] };
+        modified = model.modify(obj, { $pop: { arr: 1 } });
+        assert.deepEqual(modified, { arr: [] });
+        modified = model.modify(obj, { $pop: { arr: -1 } });
+        assert.deepEqual(modified, { arr: [] });
+      });
+
+    });   // End of '$pop modifier'
+
   });   // ==== End of 'Modifying documents' ==== //