[Javascript] If,while loop, for loop,function

 
Conditional statement

Syntax:

if (      ) {

 // do this if condition value is true

} else {

 // do this if condition value is false

}

Example

var s = "a";

if ( s == "a" ) {

 // will execute this block
 // as the condition expression is true


} else {

 // will not execute this block
 // as the condition expression is not false

}

 Iteration Statement

• while loop

  Syntax:

    while ( true/false ) {
  
    }
  

  Example: Find the average of an array's elements

    var a = [1, 2, 3, 4];
    var sum = 0;
  
    var i = 0;    // 1. initialize a counter
    while ( i < a.length ) {      // 2. condition check
       sum = sum + a[i];
       i++;       // 3. increment counter (i.e. i = i + 1;)
    }
  
    var average = sum / a.length;
  
    console.log( average );
     //=> 2.5
  

• for loop

  Syntax:

    for (     ;     ;     ) {
  
    }
  

  Example: Find the average of an array's elements

    var a = [1, 2, 3, 4];
    var sum = 0;
  
    for (var i = 0; i < a.length; i++; ) {
       sum = sum + a[i];
    }
  
    var average = sum / a.length;
  
    console.log( average );
     //=> 2.5
  

Functions

Define a function

function name() {
// Our function code goes here.
}

e.g.

// Define a function
function add() {
 sum = 2 + 3;
 alert(sum);
}

// Call/Invoke/Execute the function foo
add();

Function returning a value

// Use the keyword "return" to output
function add () {
  var sum = 2 + 2;
  return sum;
}

// Call the function "add"
result = add();
alert(result); // This will alert "4"

Function with arguments

function add (a, b) {
  var sum = a + b;
  return sum;
}

// Call the function "add"
result = add(2, 3);

Alternative form

// Create a variable called add and store a function in it.
var add = function (a, b) {
  var sum = a + b;
  return sum;
};

// Call the function
result = add(2, 3);