typescript - Using an injected angular service as a dependency within a static method -

i trying use injected dependency within static method , of course injected dependency instance-scoped , can't used within static method.

here class:

@injectable() export class passwordvalidationservice {    constructor(private useraccountservice:useraccountservice) {   }    static passwordvalidator(control:abstractcontrol) {     return control       .valuechanges       .debouncetime(400)       .switchmap(()=> this.useraccountservice.checkcurrentpassword(control.value))       .map(res=> {           if (res.json() === true) {             return null;           }           else {             return {invalid: true};           }         }       );   }  } 

my question best practice in order use useraccountservice (dependency) within static method?

edit: redesigned app towards using instance methods instead of static methods follows:

here validator:

import {injectable} "@angular/core"; import {useraccountservice} "../../useraccount/useraccount.service"; import {abstractcontrol} "@angular/common"; import {observable} "rxjs/observable";   @injectable() export class passwordvalidationservice {    constructor(private useraccountservice:useraccountservice) {   }    passwordvalidator(control:abstractcontrol):observable<any> {     let validationresult = this.useraccountservice.checkcurrentpassword(control.value)       .map(res=> {           if (res.json() === true) {             return null;           }           else {             return {invalid: true};           }         }       );      return validationresult;   }  } 

here component using validator:

constructor(private router:router,               private formbuilder:formbuilder,               private stylingservice:stylingservice,               private sessionservice:sessionservice,               private passwordvalidationservice:passwordvalidationservice) {   }    ngoninit() {     this.signinform = this.formbuilder.group({       credentials: this.formbuilder.group({         username: [this.credentials.username, validators.required],         password: [this.credentials.password, [validators.required, this.passwordvalidationservice.passwordvalidator]]       })     });   } 

here error message get:

browser_adapter.ts:82 typeerror: cannot read property 'useraccountservice' of undefined     @ passwordvalidationservice.passwordvalidator (http://localhost:8080/app/shared/services/password-validation.service.js:18:36)     @ eval (http://localhost:8080/vendor/@angular/forms/src/validators.js:137:49)     @ array.map (native)     @ _executevalidators (http://localhost:8080/vendor/@angular/forms/src/validators.js:137:23)     @ formcontrol.eval [as validator] (http://localhost:8080/vendor/@angular/forms/src/validators.js:116:33)     @ formcontrol.abstractcontrol._runvalidator (http://localhost:8080/vendor/@angular/forms/src/model.js:178:56)     @ formcontrol.abstractcontrol.updatevalueandvalidity (http://localhost:8080/vendor/@angular/forms/src/model.js:164:29)     @ new formcontrol (http://localhost:8080/vendor/@angular/forms/src/model.js:304:14)     @ formbuilder.control (http://localhost:8080/vendor/@angular/forms/src/form_builder.js:36:16)     @ formbuilder._createcontrol (http://localhost:8080/vendor/@angular/forms/src/form_builder.js:68:25) 

either don't make method static or forward instance method

export class passwordvalidationservice {    constructor(private useraccountservice:useraccountservice) {   }    validate(control:abstractcontrol) {     return passwordvalidationservice.passwordvalidator(control);   }    static passwordvalidator(control:abstractcontrol) {     ...   } }