TL;DR: Use inmutable constants

問題

文脈

サンプルコード

間違い

const DISCOUNT_PLATINUM = 0.1;
const DISCOUNT_GOLD = 0.05;
const DISCOUNT_SILVER = 0.02;

//Since variables are constants we cannot reassign them
const DISCOUNT_PLATINUM = 0.05; //Error

//We can group them
const ALL_CONSTANTS = {
  DISCOUNT: {
    PLATINUM = 0.1;
    GOLD = 0.04;
    SILVER = 0.02;  
  },
};

const ALL_CONSTANTS = 3.14; //Error

ALL_CONSTANTS.DISCOUNT.PLATINUM = 0.08; //NOT AN ERROR. WTF!


const ALL_CONSTANTS = Object.freeze({
  DISCOUNT: 
    PLATINUM = 0.1;
    GOLD = 0.05;
    SILVER = 0.02; 
});

const ALL_CONSTANTS = 3.14; //Error

ALL_CONSTANTS.DISCOUNT.PLATINUM = 0.12; //NOT AN ERROR. WTF!

右

export const ALL_CONSTANTS = Object.freeze({
  DISCOUNT: Object.freeze({
    PLATINUM = 0.1;
    GOLD = 0.05;
    SILVER = 0.02;  
  }),
});

const ALL_CONSTANTS = 3.14; //Error

ALL_CONSTANTS.DISCOUNT.PLATINUM = 0.12; //ERROR

//Code works, but it is coupled and we cannot test it

Class TaxesProvider {
  applyPlatinum(product);
}

//Now we can couple to a interface (the protocol of taxes provider)
//Since class has no setters it is constant an immuatable
//And we can replace it on tests

検出

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詳しい情報

クレジット

You start digging in the code. The more you dig, the more stuff you turn up. Eventually you dig yourself into a hole you can’t get out of. To avoid digging your own grave, refactoring must be done systematically.