if (typeof(reValue) == "undefined") {
alert("undefined");
}
typeof 返回的是字符串,有六种可能:"number"、"string"、"boolean"、"object"、"function"、"undefined"
if (typeof(reValue) == "undefined") {
alert("undefined");
}
typeof 返回的是字符串,有六种可能:"number"、"string"、"boolean"、"object"、"function"、"undefined"