13-functions-param-arguments.md

Functions - arguments and parameters

• Parameters are like placeholders for data that will be passed to a function.

• Arguments are the actual values passed to a function while calling it

  function calculateBill(billAmount, taxRate) { // here billAmount, taxRate are parameters const total = billAmount + billAmount * taxRate return total; }
  
  calculateBill(100, 0.13); // here 100, 0.13 are arguments

• Parameters are variables local to the function; available only inside the function.

• You can also pass variables as arguments during a function call.

• We can also pass expressions as arguments to a function.

    myTotal3 = calculateBill(20+20+30, 0.3);
  
  

• So, we can either pass direct value or variables holding value or expressions resulting in a value to a function as arguments.

• Passing functions as arguments:

  function doctorize(name) {
    return `Dr. ${name}`;
  }
  
  function yell(name) {
    return `HEY ${name.toUpperCase()}`;
  }
  
  // We can pass a function inside another
  yell(doctorize("Soumya")); // HEY DR. SOUMYA
  // Above, returned value of doctorize function is passed to yell function

  • Default values:

    function yell(name = "Silly Goose") {
      return `HEY ${name.toUpperCase()}`;
    }
    
    yell("Soumya"); // HEY SOUMYA
    yell(); // HEY SILLY GOOSE
    
    // Above, if we don't pass any argument to yell function, then it takes the default value in function definition,
    // here Silly Goose, else it takes whatever we pass as argument.

  • Important gotcha:

    function calculateBill(billAmount, taxRate = 0.13, tipRate = 0.15) {
      console.log("Running Calculate Bill!!");
      const total = billAmount + billAmount * taxRate + billAmount * tipRate;
      return total;
    }
    
    // Suppose above, we want to pass the tipRate but not the taxRate and want taxRate to be default,
    // then the only thing we can do is:
    
    calculateBill(100, undefined, 0.66); // here the taxRate will default to 0.13 as
    // we have passed undefined to it and the tipRate will be 0.66 as passed