![20240708104204_wsyFbJsMG3.jpeg](//cdn.ppomppu1.co.kr/zboard/data3/2024/0708/20240708104204_wsyFbJsMG3.jpeg) ![20240708104206_13zPykhcIC.jpeg](//cdn.ppomppu1.co.kr/zboard/data3/2024/0708/20240708104206_13zPykhcIC.jpeg) ![20240708104205_trpOG0U56F.jpeg](//cdn.ppomppu1.co.kr/zboard/data3/2024/0708/20240708104205_trpOG0U56F.jpeg) ![20240708104207_f8Y4yx0PdD.jpeg](//cdn.ppomppu1.co.kr/zboard/data3/2024/0708/20240708104207_f8Y4yx0PdD.jpeg) ![20240708104207_QIF3Yil1VG.jpeg](//cdn.ppomppu1.co.kr/zboard/data3/2024/0708/20240708104207_QIF3Yil1VG.jpeg) (1) The ¡°let¡± and ¡°const¡± keywords were introduced in ES6. They are part of modern Javascript. And the ¡°var¡± keyword is the old way of declaring variables.
(2) ±×¸² 1: The ¡°let¡± keyword is used to declare variables that can change later during the execution of our program.
(3) ±×¸² 2: On the other hand, the ¡°const¡± keyword is used to declare variables that are not supposed to change at any point in the future. So, the value of a variable that is declared using ¡°const¡± cannot be changed, or reassigned.
(4) ±×¸² 3: This also means that empty const variable cannot be declared. When using ¡°const¡±, we basically need an initial value.
(5) As a best practice for writing clean code: It is highly recommended to 1️⃣Use ¡°const¡± by default, 2️⃣and use ¡°let¡± only when you are pretty sure that the variable needs to change at some point in the future. 👉 It¡¯s a good practice to have as little variable mutations, or variable changes, as possible. Changing variables introduces a potential to create bugs, errors in your code.
(6) Using ¡°var¡± keywords should actually be completely avoided, but we should still know how it works for legacy reasons. You will see ¡°var¡± keywords in older code bases or some older tutorials online.
(7) ±×¸² 4: ¡°var¡± is the old way of defining variables, prior to ES6. Although ¡°var¡± is very similar to ¡°let¡±, below the surface, both ¡°var¡± and ¡°let¡± are actually pretty different. And there are also many differences among all 3 of them: ¡°let¡±, ¡°const¡±, ¡°var¡±. 👉 ÀÚ¼¼ÇÑ Àǹ̴ °ÀÇ Áøµµ´ë·Î ¹è¿ì¸é ÀÚ¿¬½º·´°Ô ÀÌÇØµÉ °Í.
(8) ±×¸² 5: Not using ¡°let¡± nor ¡°const¡±, nor ¡°var¡± still works. However, doing so is somehow terrible because it doesn¡¯t create a variable in the current so-called scope. Instead, Javascript will create a property on the global object. 👉 ÀÚ¼¼ÇÑ Àǹ̴ °ÀÇ Áøµµ´ë·Î ¹è¿ì¸é ÀÚ¿¬½º·´°Ô ÀÌÇØµÉ °Í.
(9) The key takeaway: You should always properly declare variables. Never write a variable like ¡°lastName¡± without really declaring it as seen in ±×¸² 5. |