CODEWITHSUNDEEP
javascriptfunctionjavascript-function-declaration
emjKamara
emjKamara

Reputation: 31

Can some please explain to me the difference between the function keyword and const in declaring a function

As demonstrated in the below examples, I used the function keyword to declare a function that will generate a random integer number within a range, and I also used a const keyword to declare another function that will convert a string and return an integer. Your brief explanation will be helpful and appreciated.

//Generating a random whole number within a range.
function isBeginner(a1, a2) {
  let randomRange = "";
  if (a2 >= a1) {
    randomRange = Math.floor(Math.random() * (a2 - a1 + 1) + a1);
  } else {
    randomRange = Math.floor(Math.random() * (a1 - 1 + a2) - a1);
  }
  return randomRange;
};

console.log(isBeginner(2, 4)); //positive integer expected
console.log(isBeginner(5, 3)); //negative integer expected

//Using ParseInt to generate an Integer

const isBeginner2 = function(lib) {
  let crib = "";

  // using Switch statement for better descriptions
  switch (lib) {
    case "Zero before a real number":
      crib = parseInt(lib)
      break;

    case "String":
      crib = parseInt(lib);
      break;

    case "Decimal number":
      crib = parseInt(lib);
      break;

    case "Letter before a number":
      crib = parseInt(lib);
      break;

    case "Number before a letter":
      crib = parseInt(lib);
      break;

    default:
      crib = parseInt(lib);
      break;

  }
  return crib;
};

console.log(isBeginner2(005)); // output **5** expected
console.log(isBeginner2("Stay Healthy")); // output **NaN** expected
console.log(isBeginner2(1.5)); // output **1** expected
console.log(isBeginner2("E7")); // output **NaN** expected 
console.log(isBeginner2("8S")); // output **8** expected

Upvotes: -2

Views: 89

Answers (2)

Scott Marcus
Scott Marcus

Reputation: 65853

The two syntaxes you show represent a "function declaration" and a "function expression".

Function Declaration:

function foo(){

}
  • A function declaration (also known as a function statement) declares a function with the function keyword. The function declaration must have a function name.
  • Function declarations do not require a variable assignment as they are standalone constructs and they cannot be nested inside a functional block.
  • These are executed before any other code.
  • The function in the function declaration can be accessed before and after the function definition (due to "hoisting").

Function Expression:

[var, let, const] functionName = function(){

}
  • A function Expression is similar to a function declaration but without the function name (an anonymous function assigned to a variable).
  • Function expressions can be stored in a variable assignment.
  • Function expressions load and execute only when the program interpreter reaches the line of code.
  • The function in the function expression can be accessed only after the function definition (the variable is hoisted, but the actual assigned value is not).

Now whether you use var, let, or const in the function expression doesn't really affect how the function operates, but it does affect the scope of the function, and in the case of const indicates that the variable can't be reassigned.

Upvotes: 2

Yevhen Lebid
Yevhen Lebid

Reputation: 11

Function expressions

  • Functions are values. They can be assigned, copied or declared in any place of the code.
  • If the function is declared as a separate statement in the main code flow, that’s called a “Function Declaration”.
  • If the function is created as a part of an expression, it’s called a “Function Expression”.
  • Function Declarations are processed before the code block is executed. They are visible everywhere in the block. Function Expressions are created when the execution flow reaches them.

Upvotes: 0

Related Questions