Combination mode

• Combination pattern is to combine objects into a tree structure to represent the "part-whole" hierarchical structure. Furthermore, it uses the polymorphism of objects to treat the combination objects and individual objects in a unified way.

• Note:

  • Combination patterns are not paternity
  • Consistency of Leaf Object Operations
  • Bidirectional mapping relationship
  • Improving the Performance of Composite Patterns by Using Responsibility Chain Patterns

• Application scenario

  • Part-Whole Hierarchy Representing Objects
  • Customers want to treat all objects in the tree uniformly

• Examples: Scanning folders

  /* * * * * * Folder****** */
  var Folder = function(name) {
      this.name = name;
      this.files = [];
      this.parent = null;
  }
  
  Folder.prototype.add = function(file) {
      file.parent = this;
      this.files.push(file);
  }
  
  Folder.prototype.scan = function() {
      console.log('Start scanning folders:' + this.name);
      var i = 0,
          len = this.files.length,
          file;
      
      for(; i < len; i++) {
          file = this.files[i];
          file.scan();
      }
  }
  
  Folder.prototype.remove = function() {
      if (!this.parent) {
          return;
      }
      var i = this.parent.files.length - 1,
          files = this.parent.files,
          file;
  
      for(; i >= 0; i--) {
          file = files[i];
          if (file === this) {
              files.splice(i, 1);
          }
      }
  }
  
  /* * * * * * File****** */
  var File = function(name) {
      this.name = name;
      this.parent = null;
  }
  
  File.prototype.add = function() {
      throw new Error('No more files can be added under the file');
  }
  
  File.prototype.scan = function() {
      console.log('Start scanning files:' + this.name);
  }
  
  File.prototype.remove = function() {
      if (!this.parent) {
          return;
      }
      var i = this.parent.files.length - 1,
          files = this.parent.files,
          file;
  
      for(; i >= 0; i--) {
          file = files[i];
          if (file === this) {
              files.splice(i, 1);
          }
      }
  }