Karma或TypeScript编译器告诉我类型'String'上不存在属性'padStart'

Question

I have a Angular 7 project with with lib=es2015 and target=es2015, and Angular-CLI compiling and the app running are very much OK. However, when running unit tests with ng test , Karma or TypeScript compiler told me Property 'padStart' does not exist on type 'String'

27 03 2019 10:40:57.424:INFO [karma-server]: Karma v4.0.1 server started at http://0.0.0.0:9876/
27 03 2019 10:40:57.424:INFO [launcher]: Launching browsers Chrome with concurrency unlimited
27 03 2019 10:40:57.429:INFO [launcher]: Starting browser Chrome
ERROR in node_modules/@azure/storage-blob/lib/utils/utils.common.ts(300,24): error TS2339: Property 'padStart' does not exist on type 'String'.
node_modules/@azure/storage-blob/lib/utils/utils.common.ts(301,26): error TS2339: Property 'padStart' does not exist on type 'string'.

When checking the offending codes as indicated in the error message:

export function padStart(
  currentString: string,
  targetLength: number,
  padString: string = " "
): string {
  if (String.prototype.padStart) {
    return currentString.padStart(targetLength, padString);
  }
...

I find that the last 2 lines of codes are looking perfectly fine to me, since I understand that padStart is defined in es2017, so the programmers of the lib had crafted those. If in tsconfig.json I have lib=es2017 and target=es2015, the compiling of ng test is fine.

I like to find out the cause of the problem, and the suspects are: Type Script compiler, Karma, Angular compiler, or the offending codes. Which one do you think?

Answer 1

If in tsconfig.json I have lib=es2017 and target=es2015, the compiling of ng test is fine

This is the correct fix. padStart only came with ES2017 : https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart