直接看代码:
console.log(typeof 42);
// expected output: "number"
console.log(typeof 'blubber');
// expected output: "string"
console.log(typeof true);
// expected output: "boolean"
var test;
console.log(typeof test);
// expected output: "undefined"
console.log(test);
// expected output: undefined
if(test != undefined){
console.log("已定义")
}else {
console.log("未定义");// expected output: 未定义
}
if(typeof(test) != "undefined"){//typeof() 返回的值是字符串
console.log("已定义");
}else{
console.log("未定义");// expected output: 未定义
}
typeof() 返回的值是字符串