Function

Function

1. Definition

   • functionName(parameters){ code to execute }
   • var x = function(parameters) { code to execute }
   • EX: addNumber(a, b){ return a + b) }; x=addNumber(1,2)

2. Parameter

   • Parameter vs argument
     • Paramter: names listed in function definition
     • Arument: real value passed to function
   • Parameter rules
     • not specify type
     • not perform type check on passed argument
     • not check number of argument received
   • Argument object
     • use when: too many arguments (more than declared)
     • arguments.length; arguments[i]
   • Cach truyen gtri
     • by value = arguments
     • by reference = object

3. Closures

   • Global variables
     • lifetime: as long as application lives
     • all variable declare without var --> global variable (even if inside function)
   • Local variables = closure

4. Invocation (goi ham)

   • goi giong o EX phan definition
   • Method of object: objectName.functionName();
   • function constructor
     • function myFunction(ar1, arg2){ this.firstName = arg1; this.lastName = arg2;}
     • var x = myFunction("John", "Joe"); x.firstName;
   • use function method
     • call()
       • var number; function myFunction(a,b){ return a*b;} number = myFunction.call(number, 10, 2)
     • apply()
       • var number, myArray; function myFunction(a,b){ return a*b;} myArray = [10,2]; number = myFunction.apply(number,myArray)

5. Recursion = De quy

   • Syntax
     • Loop: var factor = function(number) { var result = 1; var count; for (count = number; count > 1; count--) { result *= count; } return result; }; console.log(factor(6)); // 720
     • Recursion: var countdown = function(value) { if (value > 0) { console.log(value); return countdown(value - 1); } else { return value; } }; countdown(10);
   • feature
     • call itself
     • 10 times slower than loop
     • s.times solve problem easier than loop
   • use for
     • iterative branching
     • such as: fractal math, sorting, or traversing the nodes of complex or non-linear data structures