Unable to pass records array to apex. Records are going with null value fields

Question

Above error is coming in console.

Below is the code:

@track calculateTotal;
@track error;
@track results;
@track _shippingcharges;
@track _salestax;
@track _productarray;

@api set shippingcharges(value) {
    this._shippingcharges = value;
    this.doCalc();
}
get shippingcharges() {
    return this._shippingcharges;
}
@api set salestax(value) {
    this._salestax = value;
    this.doCalc();
}
get salestax() {
    return this._salestax;
}
@api set productarray(value) {
    this._productarray = value;
    this.doCalc();
}
get productarray() {
    return this._productarray;
}
doCalc() {
    if ((this.shippingcharges !==undefined) && (this.salestax !== undefined) && (JSON.parse(JSON.stringify(this.productarray)) !== undefined)) {
        console.log(this.shippingcharges);
        console.log(this.salestax);
        console.log(JSON.parse(JSON.stringify(this.productarray))); // getting error on using JSON
        console.log('I am in doCalc');
        calculateTotal({ shippingcharges: this.shippingcharges, salestax: this.salestax, pricebookProductArray: JSON.parse(JSON.stringify(this.productarray)) })
            .then(result => {
                this.calculateTotal = result;
            })
            .catch(error => {
                this.error = error;
            });
    
    }
}

Also, records in productArray are going to apex, but with all fields null. (the main problem)

Below is apex method:

@AuraEnabled(cacheable=true)
    public static decimal calculateTotal(Decimal shippingcharges, Decimal salestax, List<PriceBookEntry2> pricebookProductArray){
        System.debug(shippingcharges);
        System.debug(salestax);
        System.debug(pricebookProductArray);
        Decimal total = 0;
        Decimal calculatedPrice = 0;
        for(PriceBookEntry2 pbe : pricebookProductArray){
            System.debug('pbe.subtotal:'+pbe.subtotal);
            total = total + pbe.subtotal;
        }

        system.debug('total:'+total);

        calculatedPrice = total + salestax + shippingcharges;

        return calculatedPrice;  
        
    }

public class PriceBookEntry2{
         @AuraEnabled
         public String priceBookEntryId; 
         @AuraEnabled
         public String productId; 
         @AuraEnabled
         public String productName; 
         @AuraEnabled
         public String productCode;
         @AuraEnabled
         public String priceBookId;
         @AuraEnabled
         public String priceBookName;
         @AuraEnabled
         public Decimal priceUnit; 
         @AuraEnabled
         public Integer quantity;
         @AuraEnabled
         public Decimal subtotal;

         
         public PriceBookEntry2(){
             priceUnit = 0;
             quantity = 0;
             subtotal = 0;
         }
    }
    }

Answer 1

(JSON.parse(JSON.stringify(this.productarray))

will always return a string, so you're entering your if block too early. Rewrite your if as:

if(typeof this.shippingcharges == "number" && typeof this.salestax == "number" && this.productarray instanceOf Array) {