无法获取变量中的数组值 - angular

Question

简要说明： 我使用 **js**.

在变量 res 中获取了结果

res 在控制台上的结果如下所示。

see here

Requirement: I want to get the value of res in angular variable. I have declared

resarry = [];

当我做的时候

this.resarry = res;
console.log(this.resaary);

出现错误 - 无法设置未定义的'resarray` 属性。

console.log(results); // no problem in this line console.log(this.resarry); // giving error

export class HomePage {
resarry = [];


constructor(){
     var connection = new JsStore.Instance();
              var dbName = 'Demo';
          connection.openDb(dbName);

          connection.select({
            from: Test1,
          }).then(function(res) {
         // results will be array of objects

            console.log(res,'results');
            this.resarry = results;
console.log(results); // no problem in this line
console.log(this.resarry); // giving error

          }).catch(function(err) {
            console.log(err, 'error');
            alert(err.message);
        });

}
}

Answer 1

resarry:number[] = new Array();

将初始化一个未定义的空数组。

您可以设置预期结果的类型。

Answer 2

变化：

connection.select({
  from: Test1,
}).then(function(res) {
  // ...
});

至：

connection.select({
  from: Test1,
}).then(res => {
  // ...
});

基本上，function() { ... } 无法从外部作用域访问 this，而箭头函数可以。可以找到更深入的解释 here.

此外，arrow functions' docs。

Answer 3

connection.select({
         from: Test1,
      }).then(function(res) { // results will be array of objects
        console.log(res,'results');
        this.resarry = results; //  perhaps like that => this.resarry = res
        console.log(results); // i think, you should have an error on this line because **results** isn't a variable but a string in your console
        console.log(this.resarry); // giving error

      })

Answer 4

因为，"this" 意味着是当前函数对象。所以你在构造函数中使用的 "this" 并不是实际的组件

使用箭头函数或

constructor(){
     var connection = new JsStore.Instance();
              var dbName = 'Demo';
          connection.openDb(dbName);
     var $this = this;
          connection.select({
            from: Test1,
          }).then(function(res) {
         // results will be array of objects

            console.log(res,'results');
            $this.resarry = results;
console.log(results); // no problem in this line
console.log($this.resarry); // giving error

          }).catch(function(err) {
            console.log(err, 'error');
            alert(err.message);
        });

}

Answer 5

用户箭头函数以及打字稿类型在分配之前验证事物

export class HomePage {
    resarry: any[] = []; //--> resarry: any[] -> used to set the type as array
    constructor() {
        let connection = new JsStore.Instance(); //-> use Let insted of Var
        let dbName = 'Demo';
        connection.openDb(dbName);
        connection.select({
            from: "Test1",
        }).then(res => {
            console.log(res);
            if (res)
                if (res.length > 0){
                    this.resarry = res;
                    console.log(this.resarry);
                    console.log("connection Successful with array objects");
                }else{
                    console.log("connection Successful  without array objects");
                }
        }), err => {
            console.log("connection error");
        };

    }
}

无法获取变量中的数组值 - angular

Cannot fetch array value in variable - angular

javascript

ionic-framework

ionic2

ionic3

angular