Voice of a Developer: Part Ten - JavaScript Functions

• Voice of a Developer: JavaScript Data Types - Part One
• Voice of a Developer: JavaScript Objects - Part Two
• Voice of a Developer: JavaScript Engines - Part Three
• Voice of a Developer: JavaScript Common Mistakes - Part Four
• Voice of a Developer: Editors - Part Five
• Voice of a Developer: VSCode - Part Six
• Voice of a Developer: Debugging Capabilities of VSCode - Part Seven
• Voice of a Developer: Part Eight - JavaScript OOP
• Voice of a Developer: Part Nine - JavaScript Useful Reserved Keywords

Properties of function

• Call v/s Apply

  If you want to assign the value of a function we use straight forward way, i.e.,
  1. var val = myFunction (2,3); // val = 6
  There are two other way to achieve it using call or apply property,
  1. var val = 0;
  2. myFunction.apply(val, [2, 3]); // 6 as output
  3. myFunction.call(val, 2, 3); // 6 as output

  The call requires the parameters be listed explicitly

  Apply lets you invoke the function with arguments as an array.

• The "constructor" property

  Every object has a built-in property named constructor. It refers to the function which created it. Let us understand in detail:
  1. function myFunction(a, b) {
  2. return a * b; // Function returns the multiplication of a and b
  3. }
  4. var m = new myFunction();
  5. console.log(m.constructor == myFunction); // true
  6. console.log(m.__proto__.constructor == myFunction); // true, the other way to check is

• Defining Your Own Function Properties

  Many times we need a unique number say GUID or identifies which increments with each call made to function. In such a scenario, it is recommended to attach a property with a function. It is acting like a static property to keep track of the last value returned.
  1. function myFunction(a, b) {
  2. ++myFunction.p1;
  3. return a * b; // Function returns the multiplication of a and b
  4. }
  5. myFunction.p1 = 1;
  6. myFunction();
  7. myFunction.p1; // will print 2

• Length property

  In a function, we pass arguments to process input, and sometimes we don’t pass the correct number of arguments. Therefore, it is good practice to check the required number of arguments needed for a particular function.
  1. function myFunction(a, b) {
  2. return a * b;
  3. }
  4. myFunction(2); // will give NaN because b is undefined
  5. Its time to fix above
  6. function by using property length
  8. function myFunction(a, b) {
  9. var argsRequired = arguments.length;
  10. var argsActual = arguments.callee.length;
  11. if(argsRequired != argsActual) {
  12. throw new Error("Wrong # of args passed");
  13. }
  14. return a * b;
  15. }