Function Declarations vs. Expressions

Function declaration은 function을 declare하기 전에 call할 수 있음

Expression은 그렇게 안됨 🙅‍♀️

Expression은 declare하기 전에 해당 function을 call하면 에러 뜸

e.g. Uncaught ReferenceError: Cannot access 'OOO' before initialization

 

// Function declaration
function calcAge1(birthYear) {
    return 2037 - birthYear;
}
const age1 = calcAge1(1991);

// Function expression
// Expression produces value
// Functions are not type, but value storing a variable
const calcAge2 = function (birthYear) {
    return 2037 - birthYear;
}
const age2 = calcAge2(1991);

console.log(age1, age2);
// prints 46 46