Method cache

src/js/tether.js:225–237

(k, getter)

  }

  cache(k, getter) {
    // More than one module will often need the same DOM info, so
    // we keep a cache which is cleared on each position call
    if (isUndefined(this._cache)) {
      this._cache = {};
    }

    if (isUndefined(this._cache[k])) {
      this._cache[k] = getter.call(this);
    }

    return this._cache[k];
  }

  enable(pos = true) {
    const { classes, classPrefix } = this.options;