async functions(handlerPropertyName = 'handler') {
    if (this._functions) {
      return this._functions
    }

    const functions = this.options.function
      ? {
          [this.options.function]: this.serverless.service.getFunction(
            this.options.function,
          ),
        }
      : this.serverless.service.functions

    const functionsToBuild = {}

    for (const [alias, functionObject] of Object.entries(functions)) {
      const shouldBuild = await this._shouldBuildFunction(
        functionObject,
        handlerPropertyName,
      )
      if (shouldBuild) {
        functionsToBuild[alias] = functionObject
      }
    }

    this._functions = functionsToBuild

    return functionsToBuild
  }
Get a record of functions that should be built by esbuild