tsc 命令和 tsconfig watch 之间的区别：Typescript 中的 true？

Question

I created tsconfig.json, and in compiler options i set watch:true; then in index.ts file I write this code:

async function test2(){
   return 'hello world'
}

Typescript compiler automatically created index.js file, with this code:

async function test2(){
   return 'hello world'
}

But when I run tsc index.ts compiler added this code to js file:

var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
    function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
    return new (P || (P = Promise))(function (resolve, reject) {
        function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
        function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
        function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
        step((generator = generator.apply(thisArg, _arguments || [])).next());
    });
};
var __generator = (this && this.__generator) || function (thisArg, body) {
    var _ = { label: 0, sent: function() { if (t[0] & 1) throw t[1]; return t[1]; }, trys: [], ops: [] }, f, y, t, g;
    return g = { next: verb(0), "throw": verb(1), "return": verb(2) }, typeof Symbol === "function" && (g[Symbol.iterator] = function() { return this; }), g;
    function verb(n) { return function (v) { return step([n, v]); }; }
    function step(op) {
        if (f) throw new TypeError("Generator is already executing.");
        while (_) try {
            if (f = 1, y && (t = op[0] & 2 ? y["return"] : op[0] ? y["throw"] || ((t = y["return"]) && t.call(y), 0) : y.next) && !(t = t.call(y, op[1])).done) return t;
            if (y = 0, t) op = [op[0] & 2, t.value];
            switch (op[0]) {
                case 0: case 1: t = op; break;
                case 4: _.label++; return { value: op[1], done: false };
                case 5: _.label++; y = op[1]; op = [0]; continue;
                case 7: op = _.ops.pop(); _.trys.pop(); continue;
                default:
                    if (!(t = _.trys, t = t.length > 0 && t[t.length - 1]) && (op[0] === 6 || op[0] === 2)) { _ = 0; continue; }
                    if (op[0] === 3 && (!t || (op[1] > t[0] && op[1] < t[3]))) { _.label = op[1]; break; }
                    if (op[0] === 6 && _.label < t[1]) { _.label = t[1]; t = op; break; }
                    if (t && _.label < t[2]) { _.label = t[2]; _.ops.push(op); break; }
                    if (t[2]) _.ops.pop();
                    _.trys.pop(); continue;
            }
            op = body.call(thisArg, _);
        } catch (e) { op = [6, e]; y = 0; } finally { f = t = 0; }
        if (op[0] & 5) throw op[1]; return { value: op[0] ? op[1] : void 0, done: true };
    }
};

function test2() {
    return __awaiter(this, void 0, void 0, function () {
        return __generator(this, function (_a) {
            return [2 /*return*/, 'string'];
        });
    });
}

So question is, what is difference between tsc and watch:true? Why tsconfig.json's watch:true mode just copying same code as I wrote in ts file to js. but when I run tsc index.ts it creates such a mess? Do I need every time run tsc to new ts files? (bcz watch: true in tsconfig.json, if I understand it right, must compile the typescript code into javascript automatically) What is the difference between tsc index.ts and watch:true in tsconfig?

Answer 1

I just found out, that watch: true, here in tsconfig.json, really compiles ts code to js (and compiles depending on which version of js you choose in target field). tsc index.ts command on another hand, compiles code to old es3-5

{
    "compilerOptions": {
        "target": "esnext",
        "watch": true

    }
}