LOOPS IN JAVASCRIPT

A loop allows us to repeat or execute a set of statement multipel times, which are written inside a loop. It execute a block of code many times. Just like all other programming languages javascript also support looping concept.

javascript contain following types of loops :-

• for loop
• do...while loop
• while loop
• for...in loop

FOR LOOP

The for loop consist of three expressions, with in brackets and separated by semicolons.

for loop syntax

for(initialisation;testcondition;increment/decrement)
 {
     statement;
}

for eg :-

var temp = 0;
for (var i = 1; i <= 20; i++)
{
   temp = temp + i;
}
alert("Sum = " + temp);   

do while loop

The do while loop execute a set of statement atleast once, whether condition is true or not, after executing statement atleast once, then it check the condition if the condition get true, then loop get repeated until condition is true.

do while loop syntax

do {
     statement to executed;
     increment/decrement;
}
while (condition);
}

for eg:-

var temp = 0;
var number = 1;
do {
   temp += n;         // -- statement
   n++;              // -- increment/decrement
} while (n <= 20);   // -- condition
alert("Sum = " + temp);   

while loop

Unlike do while loop which execute atleast once wheather condition is true or false, while loop only execute statement if condition get true and continue this process until condtion is true.

while loop syntax

while (condition) {
    statement to be executed
}

for eg:-

 var temp = 0;
    var n = 1;
    while (n <= 50) {  // -- condition
      temp += n;        // -- statement
      n++;             // -- increment/decrement
     }
    alert("Sum = " + temp);  

for..in loop

for..in loop iterates through the properties of an object .

syntax of for..in loop

for (var in object) {
  statement to execute;
}

for eg:-

var employee = { name:"suresh", age: 25, degree: "btech" };
for (var item in employee) {
   alert(employee[item]);  
}