関連ワード:  javascript if not undefined or null    javascript is not undefined or null    javascript check if not undefined or null    javascript check if variable is not undefined or null    javascript check if object not undefined or null    javascript check value is not undefined or null    javascript is not null or undefined or empty    javascript check if not null or undefined or empty    javascript check if variable is not null or undefined or empty string    javascript check if string is not null or undefined or empty