如何从数组的ForEach循环中的TypeScript类中引用此父方法？

Question

因此，我试图从数组的ForEach循环中调用TypeScript类中的方法。但是，似乎我无法弄清楚如何为父类确定正确的“ this”范围。

我想做的是从Survey.answerKey.q2SelectedValues.forEach（function（value（））{...}）中调用getFeatureAmount方法；像这样：

export class CalculationService {
        private _baseRate: BaseRate;
        private _subtotalPlatform: number = 0; 

        constructor(){
            this._baseRate = new BaseRate(125, 60);
        };

       //This is the method I'm trying to call
        private getFeatureAmount = (value: string, sub: number): number => {
            return sub += parseInt(value) * this._baseRate.local; 
        }

        public calculate(survey: Survey){

        let subtotal_ui: number = 0;
        subtotal_ui = (parseInt(survey.answerKey.q1SelectedValues[0]) * 5);

        survey.answerKey.q2SelectedValues.forEach(function(value){
            subtotal_ui = this.getFeatureAmount(value, subtotal_ui); //ERROR HERE. 'this' is undefined
        });

        return subtotal_ui + this._subtotalPlatform;
    }
}

但是我知道'this'是未定义的，找不到getFeatureAmount。作为临时的解决方法，我必须将getFeatureAmount用作回调函数。

private getFeatureAmount = (value: string): number => {
            return this._subtotalPlatform += parseInt(value) * this._baseRate.local; 
        }

survey.answerKey.q2SelectedValues.forEach(this.getFeatureAmount);

这不是我真正想做的。所以我想知道有什么方法可以使用lambda（）=> {}吗？

Answer 1

尝试改变

survey.answerKey.q2SelectedValues.forEach(function(value){
   subtotal_ui = this.getFeatureAmount(value, subtotal_ui); //ERROR HERE. 'this' is undefined
})

至

survey.answerKey.q2SelectedValues.forEach((value) => {
   // now this will be refer to the instance of your CalculationService class
   subtotal_ui = this.getFeatureAmount(value, subtotal_ui);
});