Angular 2 - Constructing dates in constructor - Error: Type 'Date' cannot be assigned to type 'string'

In my attempt to generate a fresh date object for an ngx-chart by referencing this specific example, I came across the following code snippet:

  constructor() {
    this.data = this.multi.map(group => {
      group.series = group.series.map(dataItem => {
        dataItem.name = new Date(dataItem.name);
        return dataItem;
      });
      return group;
    });
    console.log(this.data);
  }

While I comprehend the usage of new Date() as demonstrated here, I am consistently encountering the error message: "Type 'Date' is not assignable to type 'string'." It is clear that this issue arises due to TypeScript, but what eludes me is how to effectively manage these two in conjunction. Other instances I've come across did not seem to experience such a hindrance.

Answer №1

This situation involves type inference in TypeScript. When you use double quotes for 'name', TS automatically infers it as a string. To specify that this should be of any type, you need to explicitly define it.

To address this issue, you can create an interface like the following:

interface Multi{
  name:String
  series: Array<{value: number, name: any}>
}

Then, apply it as shown below:

export var multi: Multi[] = [
  {
    "name": "Tunisia",
    "series": [
      {
        "value": 3309,
        "name": "2016-09-19T10:24:08.741Z"
      }
      ...
    ]
  },
  {
    "name": "El Salvador",
    "series": [
      {
        "value": 5714,
        "name": "2016-09-19T10:24:08.741Z"
      },
      ....
    ]
  }
]

Another approach is to simplify the syntax in Plunker to make sure TS understands it correctly:

 this.data = multi.map(group => 
       <any>{ // Indicate that this is explicitly any
         "name": group.name,
         "series": group.series.map(s => <any>{"value":s.value, "name":new Date(s.name)})
       });

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