打字稿保证在.then之后丢失值

Question

我在Angular2服务中有一个函数,它返回Mock数据Promise.resolve,当解包时.then给我一个空的promise对象.我可以看到调用函数在__zone_symbole__value传递到.then however inside of.then 之前在属性中接收带有有效负载的PromiseI seem to be left with just an empty promise.

  getTemperatureData(): Promise<any> {

    let data = this.convertJSONToGoogleChartTable(temperatureData_JSON);
    let p = Promise.resolve(data);
    return p;
  }

使用Chrome我看到上面的p看起来像

ZoneAwarePromise {__zone_symbol__state: true, __zone_symbol__value: "[["Date","Temperature","LowTemperature"],["05/11/2…",69.02,null],["06/11/2016 23:54:34",69.99,null]]"}

调用代码分为两行进行调试.

getTemperatureData() {
    var d = this.dataService.getTemperatureData();
    d.then(data => this.line_ChartData = data);
}

当我看到d时,我看到与上面的p相同

ZoneAwarePromise {__zone_symbol__state: true, __zone_symbol__value: "[["Date","Temperature","LowTemperature"],["05/11/2…",69.02,null],["06/11/2016 23:54:34",69.99,null]]"}

问题发生.then在"d"的值只是一个空的承诺的地方.以下内容取自Chrome开发工具控制台,以显示我所看到的内容.

d.then(data => console.log(data))
ZoneAwarePromise {__zone_symbol__state: null, __zone_symbol__value: Array[0]}

无论我做了什么以及我尝试了多少组合,我都无法获得d中的数据.(注意,p和d只是临时破坏代码的.)

我的package.json如下:

{
  "name": "angular2",
  "version": "0.0.0",
  "license": "MIT",

  "angular-cli": {},
  "scripts": {
    "start": "ng serve",
    "lint": "tslint \"src/**/*.ts\"",
    "test": "ng test",
    "pree2e": "webdriver-manager update",
    "e2e": "protractor"
  },
  "private": true,
  "dependencies": {
    "@angular/common": "~2.1.0",
    "@angular/compiler": "~2.1.0",
    "@angular/core": "~2.1.0",
    "@angular/forms": "~2.1.0",
    "@angular/http": "~2.1.0",
    "@angular/material": "^2.0.0-alpha.9-3",
    "@angular/platform-browser": "~2.1.0",
    "@angular/platform-browser-dynamic": "~2.1.0",
    "@angular/router": "~3.1.0",
    "core-js": "^2.4.1",
    "ng2-bootstrap": "^1.1.16",
    "node-mysql": "^0.4.2",
    "rxjs": "5.0.0-beta.12",
    "ts-helpers": "^1.1.1",
    "zone.js": "^0.6.23"
  },
  "devDependencies": {
    "@types/jasmine": "^2.2.30",
    "@types/node": "^6.0.42",
    "angular-cli": "1.0.0-beta.19-3",
    "codelyzer": "1.0.0-beta.1",
    "jasmine-core": "2.4.1",
    "jasmine-spec-reporter": "2.5.0",
    "karma": "1.2.0",
    "karma-chrome-launcher": "^2.0.0",
    "karma-cli": "^1.0.1",
    "karma-jasmine": "^1.0.2",
    "karma-remap-istanbul": "^0.2.1",
    "protractor": "4.0.9",
    "ts-node": "1.2.1",
    "tslint": "3.13.0",
    "typescript": "~2.0.3",
    "webdriver-manager": "10.2.5"
  }
}

Answer 1

数据的价值只是一个空洞的承诺

这告诉我这convertJSONToGoogleChartTable是返回一个承诺，而你并没有将你的承诺链接到它上面。

请注意，如果您使用比 更强的类型any，TypeScript 编译器可能会为您捕获此问题。

由于您在获取数据后没有执行任何操作，因此您可以这样做：

  getTemperatureData(): Promise<any> {
    return this.convertJSONToGoogleChartTable(temperatureData_JSON);
  }

但是如果你想在返回数据之前对其进行一些操作，你可以在 a 中执行此操作then，链接到原始承诺：

  getTemperatureData(): Promise<any> {
    return this.convertJSONToGoogleChartTable(temperatureData_JSON)
        .then(data => {
            console.log(data);
            return data;
        });
  }