只有在第一个方法完成后才能调用另一个方法

Question

I have a situation where I need to use array in a method, which is previously populated in first method.

I need both methods to execute on componentDidMount , for example load countries, after that load towns for current country in droopdown. It goes something like that.

Lets say I need to call this 2 methods separately:

async componentDidMount() {
      this.loadCountries();
      this.loadCities(this.state.currentCountry.id);
}

How can I be sure first method is done with executing because I need to use countries array countries[], in my second method.

Right now I have situation data is retrieved from a server but second method is not aware of it becasue data are retrieved asynhronous probably, and that's it..

Thanks guys

Cheers

Answer 1

You can use the async/await method to call second function only after first function get complete .

here is your snippet .

var countries = [];
    async componentDidMount() {
         await this.countries = this.loadCountries(); // you will have countries values in 'this.countries'. Which you can access it further . 
         await this.loadCities(this.state.currentCountry.id);
    }

Answer 2

如果您在第一种方法中返回的是coutries []的全局列表，则第二种方法将知道