have two functions which , first function returns the result which stored in a variable, the same returned result variable passed as parameter in second function to hit the service. as explained code below , the two functions are invoked on ongonit , as a sequence the second function not able to catch the result of variable returned from function.Is there a way to over come this?

TS code: 

```
udata:string;

ngOninit(){
    this.f1();
    this.f2();
}

f1(){
    this.service.getudata().subscribe(res => {
        this.udata = res;
    });
}

f2(){
    this.service.getudatas(this.udata).subscribe(res => {
        const data = res;
    });
}

```