---
robots: noindex, nofollow
tags: refactoring
---

# Replace Parameter with Query

> 練習用的 [REPL](https://repl.it/@yaosiang/ReplaceParameterwithQuery)

class Order {
    get finalPrice() {
        const basePrice = this.quantity * this.itemPrice;
        let discountLevel;
        if (this.quantity > 100) discountLevel = 2;
        else discountLevel = 1;
        return this.discountedPrice(basePrice, discountLevel);
    }

    discountedPrice(basePrice, discountLevel) {
        switch (discountLevel) {
            case 1:
                return basePrice * 0.95;
            case 2:
                return basePrice * 0.9;
        }
    }
}

先用 `Replace Temp with Query` 處理 discountLevel。

class Order {
    get finalPrice() {
        const basePrice = this.quantity * this.itemPrice;
        return this.discountedPrice(basePrice, this.discountLevel);
    }

    get discountLevel() {
        return (this.quantity > 100) ? 2 : 1;
    }

    discountedPrice(basePrice, discountLevel) {
        switch (this.discountLevel) {   // 直接 query 即可
            case 1:
                return basePrice * 0.95;
            case 2:
                return basePrice * 0.9;
        }
    }
}

由於 discountLevel 可以直接查詢，就不用當參數來傳遞了。

class Order {
    get finalPrice() {
        const basePrice = this.quantity * this.itemPrice;
        return this.discountedPrice(basePrice);     // 刪除參數
    }

    get discountLevel() {
        return (this.quantity > 100) ? 2 : 1;
    }

    discountedPrice(basePrice) {                    // 刪除 discountLevel 參數
        switch (this.discountLevel) {
            case 1:
                return basePrice * 0.95;
            case 2:
                return basePrice * 0.9;
        }
    }
}