將承諾鏈分解為單獨的功能

Question

分為兩個功能：

public valJson(json, schemaFile: string) {
    return new Promise((resolve, reject) => {
        this.http.get(schemaFile)
            .toPromise()
            .then(fileContents => fileContents.json())
            .then((schema) => {
                let ajv = new Ajv({allErrors: true});
                ajv.validate(schema, json) ? 
                resolve() :
                reject(new Error("JSON does not conform to schema: " + ajv.errorsText()));
            }, err => reject(
                new Error("Unable to get schema file contents:" + err))
            );
    });
};

這個函數確實做了三件事，所以單元測試不是很好。

1. 獲取文件內容
2. 將它們解析為 json
3. 驗證json

如何將其分解以使每個任務都可進行單元測試？

嘗試 1 打破實際的驗證部分並不順利：

public valJson(json, schemaFile: string) {
    return new Promise((resolve, reject) => {
        this.http.get(schemaFile)
            .toPromise()
            .then(fileContents => fileContents.json())
            .then((schema) => {
                this.valJ(schema)
            }, err => reject(
                new Error("Unable to get schema file contents:" + err))
            );
    });
};

    valJ(schema, json) {
        let ajv = new Ajv({ allErrors: true });
        if ajv.validate(schema, json) 
            return resolve()
        reject(new Error("JSON does not conform to schema: " + ajv.errorsText()));
    }
}

更新 - 根據反饋，我試圖停止使用匿名函數，然后我將嘗試不創建新的承諾。 我在這：

public valJson(json, schemaFile: string) {
    return new Promise((resolve, reject) => {
    var getFilePromise = this.http.get(schemaFile)
            .toPromise();
    var parseToJsonPromise = getFilePromise
            .then(contents => this.toJson(contents));
    var validateJsonPromise = parseToJsonPromise.then(schema => this.valJ(schema, json, resolve, reject),
            err => reject(
                new Error("Unable to get schema file contents:" + err))
            );
    });
};

toJson(fileContents): any {
    return fileContents.json()
}

valJ(schema, json, resolve, reject): any {
    let ajv = new Ajv({ allErrors: true });
    ajv.validate(schema, json) ?
        resolve() :
        reject(new Error("JSON does not conform to schema: " + ajv.errorsText())
    );
}

Answer 1

一種可能的方法：

public valJson(json, schemaFile: string) {
  return this.fetchSchema(schemaFile)
    .then(res => this.parseSchema(res))
    .then(schema => this.validateWithSchema(json, schema));
}

fetchSchema(url) {
  return this.http.get(url).toPromise();
}

parseSchema(response) {
  return response.json();
}

validateWithSchema(json, schema) {
  let ajv = new Ajv({allErrors: true});
  if (!ajv.validate(schema, json)) {
    throw new Error("JSON does not conform to schema: " + ajv.errorsText())
  }
}