Control Statement in JavaScript

Control statement used to control the flow of execution of the program based on certain condition.
They allow program to make decision , repeat action or jump to different part of the code.

Types of statements

1. Conditional statement : used to choose execution path based on a condition. conditional/selection/decision making statement.

• if statement : If the condition is true statement will be executed. one condition - yes or no

let age = 20;
if(age >= 18){
console.log("eligible");  //eligible
}

• if else statement : If the condition is true statement will be executed otherwise else part will be execute.

let age =16;
if(age>=18){
console.log("eligible");
}
else{
console.log("not eligible"); //not eligible
}

• else if statement : If the condition is true statement will be execute if its false else if will execute if none is true then else part will execute.

let mark =75;
if(mark>=90){
console.log("A grade");
}
else if (mark>=70){
console.log("B grade");// B grade
} 
else{
console.log("C grade"); 

• Nested if statement : If statement inside another if statement. Both the condition should be true.

let age = 22;
let id = true;
if(age>=18){
if(id==true){
console.log("allowed");// allowed
}
}

• switch statement : Multiway branch statement. select a case based on a value.

let day = 2;
switch(day){
case 1 :
console.log("Monday");
break;
case 2 :
console.log("Tuesday");  //Tuesday
break;
case 3 :
console.log("Wednesday");
break;

2.Looping Statement : Used to repeat a block of code multiple times, until a condition is true.

• while loop : used to repeat/iterate a part of program repeatedly until the specified condition is true. If condition become false loop automatically stop. (no. of iteration is not fixed -we use)

let i=1;
while(i<=5){
console.log(i);  // 1 2 3 4 5
i++; 
}

• do-while loop / exit control loop : used to check the condition later, want to execute the block atleast once.

let i = 1;
do {
console.log(i); //1
i++;
}
while(i<=3);

• for loop : use to perform a task in single line. initialization, condition, increament/decreament.

for(let i=1; i<=3: i++){
console.log(i);
}

output:
1
2
3

3.Jump statement : used to break out of loops and switch statement.

• break statement : used to break the current flow of the program.

for(let i=1; i<=5; i++){
if(i===3){
break;
}
console.log(i);  //1 2
}

• continue : It doesn't break the loop, its skip the specific part of the loop and jump the next iteration of the loop.

for(let i=1; i<=5; i++){
if(i===3){
continue;
}
console.log(i);  //1 2 3 4 5
}

• return statement : ends a function and can send a value back to the place where the function was called.

function add(a, b){
return a+b;
}
let result = add(10,20);
console.log(result);  // 30