mapCall (funcName, ...args) {
    const data = []
    this.index.visitAll(function (record) {
      data.push(record[funcName](...args))
    })
    return data
  }
Return the result of calling the specified function on each record in this
collection's main index.

@method Collection#mapCall
@since 3.0.0
@param {string} funcName Name of function to call
@parama {...*} [args] Remaining arguments to be passed to the function.
@returns {Array} The result.