从外部文件在打字稿中声明var获取ReferenceError：…未定义

Question

I have the following typescript file-->

module someModule {
declare var servicePort: string;

export class someClass{
constructor(){
  servicePort = servicePort || ""; //ERROR= 'ReferenceError: servicePort is not defined'
}

also tried this on one of functions inside "someClass" -->

someFunction = () => {
    if (servicePort && servicePort != '') { //ERROR - also servicePort is not defined
            //do something with servicePort 
        }
}

If I define var servicePort somewhere on my js /html files it will work, but not all my pages contains the servicePort var, and I want to safe get the value from that varible without exception. What am I doing wrong?

Answer 1

Having a variable sometimes be defined and sometimes not is a pretty big code smell, but if you really want to do this, you need to guard access on that variable with typeof :

if (typeof servicePort !== "undefined") {
   // safe to use servicePort here
}

Note that you won't be able to tell the difference between a missing variable and one with the value undefined , but such is life.