src/utils/DomElementObjectPool.ts

   1 /**
   2  * @module xterm/utils/DomElementObjectPool
   3  * @license MIT
   4  */
   5
   6 /**
   7  * An object pool that manages acquisition and releasing of DOM elements for
   8  * when reuse is desirable.
   9  */
  10 export class DomElementObjectPool {
  11   private static readonly OBJECT_ID_ATTRIBUTE = 'data-obj-id';
  12
  13   private static _objectCount = 0;
  14
  15   private _type: string;
  16   private _pool: HTMLElement[];
  17   private _inUse: {[key: string]: HTMLElement};
  18
  19   /**
  20    * @param type The DOM element type (div, span, etc.).
  21    */
  22   constructor(private type: string) {
  23     this._type = type;
  24     this._pool = [];
  25     this._inUse = {};
  26   }
  27
  28   /**
  29    * Acquire an element from the pool, creating it if the pool is empty.
  30    */
  31   public acquire(): HTMLElement {
  32     let element: HTMLElement;
  33     if (this._pool.length === 0) {
  34       element = this._createNew();
  35     } else {
  36       element = this._pool.pop();
  37     }
  38     this._inUse[element.getAttribute(DomElementObjectPool.OBJECT_ID_ATTRIBUTE)] = element;
  39     return element;
  40   }
  41
  42   /**
  43    * Release an element back into the pool. It's up to the caller of this
  44    * function to ensure that all external references to the element have been
  45    * removed.
  46    * @param element The element being released.
  47    */
  48   public release(element: HTMLElement): void {
  49     if (!this._inUse[element.getAttribute(DomElementObjectPool.OBJECT_ID_ATTRIBUTE)]) {
  50       throw new Error('Could not release an element not yet acquired');
  51     }
  52     delete this._inUse[element.getAttribute(DomElementObjectPool.OBJECT_ID_ATTRIBUTE)];
  53     this._cleanElement(element);
  54     this._pool.push(element);
  55   }
  56
  57   /**
  58    * Creates a new element for the pool.
  59    */
  60   private _createNew(): HTMLElement {
  61     const element = document.createElement(this._type);
  62     const id = DomElementObjectPool._objectCount++;
  63     element.setAttribute(DomElementObjectPool.OBJECT_ID_ATTRIBUTE, id.toString(10));
  64     return element;
  65   }
  66
  67   /**
  68    * Resets an element back to a "clean state".
  69    * @param element The element to be cleaned.
  70    */
  71   private _cleanElement(element: HTMLElement): void {
  72     element.className = '';
  73     element.innerHTML = '';
  74   }
  75 }