javascript - Typescript module export not work when import something -

i trying create powerbi custom visual , must use typescript that. i'm not familiar typescript. got 2 ts files under same namespace(i using vs code editor):

visual.ts

module powerbi.extensibility.visual {  export class visual implements ivisual {     private target: htmlelement;     private updatecount: number;      constructor(options: visualconstructoroptions) {         console.log('visual constructor', options);         this.target = options.element;         this.updatecount = 0;     }      public update(options: visualupdateoptions) {          console.log('visual update', options);         console.log(testfunc());         $('#datepicker').datepicker();          this.target.innerhtml = `<p>update count:     <em>${(this.updatecount++)}</em></p>`;     }      public destroy(): void {         //todo: perform cleanup tasks here     }   } } 

test.ts

import react=require('react'); import reactdom=require('react-dom');  module powerbi.extensibility.visual {    export function testfunc():string{        return "test string";   }    export class testclass{} } 

problem when there no imports in test.ts can see , use exported function "testfunc()"(vs code see function) when add imports cant user function(also vs code don't recognize function)? there way have imports , use function?