Day03 - 2704.To Be Or Not To BeEASY

Description❓

Write a function expect that helps developers test their code. It should take in any value val and return an object with the following two functions.

• toBe(val) accepts another value and returns true if the two values === each other. If they are not equal, it should throw an error "Not Equal".
• notToBe(val) accepts another value and returns true if the two values !== each other. If they are equal, it should throw an error "Equal".

寫一個函數“expect”來幫助開發人員測試他們的代碼。 它應該接受任何參數“val”並返回一個具有以下兩個函數的物件：

• toBe(val) 接受另一個參數，如果兩個值彼此 === 則返回 true。 如果它們不相等，則應拋出錯誤“不等於”。
• notToBe(val) 接受另一個參數，如果兩個值 !== 彼此相等，則返回 true。 如果它們相等，它應該拋出錯誤“Equal”。

Points

• 三元運算子
• 比較運算子、邏輯運算子
• throw new Error錯誤處理

Solution✍️

[ ▶️挑戰這一題 ] [ 本日代碼 ]

1. 宣告expect函式 函式會返回 {toBe,notToBe}'兩個函式

const expect = (val1)=>{

   toBe = (val2) => {
      return  ;
   };
   notToBe = (val2) => {
      return ;
   };
   return {toBe,notToBe}
}

2. toBe,notToBe 兩個函式用三元運算子判斷val2參數與外部作用域的val1是否相符

const expect = (val1)=>{

   toBe = (val2) => {
      return val1 === val2? true : throw new Error ("Not Equal") ;
   };

   notToBe = (val2) => {
      return val1 !== val2? true : throw new Error ("Equal") ;
   };

   return {toBe,notToBe}
}

3. 修正：三元運算子返回一個表達式的值，而throw new Error是陳述句，不能直接作為表達式返回。
   因此將throw new Error用函式包裝成表達式。

const expect = (val1)=>{

   throwErr= (str)=>{
      throw new Error(str);
   }

   toBe = (val2) => {
      return val1 === val2? true : throwErr("Not Equal") ;
   };

   notToBe = (val2) => {
      return val1 !== val2? true : throwErr("Equal") ;
   };

   return {toBe,notToBe}
}

4. 參考其他solution

• 代碼更為簡潔
  • 對於邏輯比較單純的情況，可以直接在return撰寫邏輯
  • 比較運算符本身會return true，因此加上邏輯運算子處理false的結果

const expect = (val1) => {
   throwErr= (str) => {throw new Error(str)};
    
    return {
        toBe: (val2) => val2 === val1 || throwErr("Not Equal"),
        notToBe: (val2) => val2 !== val1 || throwErr("Equal"),
    };
};

Testcase

const A = expect(5);
console.log(A.toBe(5));
// console.log(A.toBe(null));
console.log(A.notToBe(null));