languageservices/expressions/src/funcs/join.ts

import {ExpressionData, Kind, StringData} from "../data";
import {FunctionDefinition} from "./info";

export const join: FunctionDefinition = {
  name: "join",
  description:
    "`join( array, optionalSeparator )`\n\nThe value for `array` can be an array or a string. All values in `array` are concatenated into a string. If you provide `optionalSeparator`, it is inserted between the concatenated values. Otherwise, the default separator `,` is used. Casts values to a string.",
  minArgs: 1,
  maxArgs: 2,
  call: (...args: ExpressionData[]): ExpressionData => {
    // Primitive
    if (args[0].primitive) {
      return new StringData(args[0].coerceString());
    }

    // Array
    if (args[0].kind === Kind.Array) {
      // Separator
      let separator = ",";
      if (args.length > 1 && args[1].primitive) {
        separator = args[1].coerceString();
      }

      // Convert items to strings
      return new StringData(
        args[0]
          .values()
          .map(item => item.coerceString())
          .join(separator)
      );
    }

    return new StringData("");
  }
};