如何检查节点js中的变量是否为空或未定义
问题描述：
我想检查我的数据是否为空或未定义，但即使我的数据不为空，我的 if 块也会执行...
I want to check my data is blank or undefined but my if block execute even my data is not blank ...
代码是:
router.post('/addNewGrade',function(req , res){
var errorMsg = [];
console.log(req.body.gradeName)
if(req.body.gradeName == '' || req.body.gradeName === undefined){
errorMsg.push("please enter grade name");
}
if(req.body.gradeDescription == '' || req.body.gradeDescription === undefined){
errorMsg.push("please enter description about your grade");
}
if(errorMsg !=''){
res.send({errorMessage :errorMsg});
return;
}
});
检查变量是否未定义的最佳方法是什么
what is the best way to check variable is undefined or not
答
因为一个未定义的变量是falsey"，你可以简单做
Because an undefined variable is "falsey", you can simple do
if (body.req.gradeName) {
// do normal stuff
} else {
// do error stuff
}
或者如果你不需要做任何事情，如果它被定义了，那么你可以做
Or if you don't need to do anything if it is defined, then you can do
if (!(body.req.gradeName)) {
// do error stuff
}