JavaScript : Switch Statement - 1

What is switch statement?

It is used for implementing a conditional construct to make logical decision.

Some of the characteristics are

• The switch statement takes an expression which is evaluated matching a series of case clauses

• The case clause should have break statement as the last instruction else the control will fall through

• The case clause can have only 1 value

• The case clause can have value of any type

• The default clause will be executed when any of the cases don't match

Use Cases

Case 1: Using switch case - fall through and grouping cases - without break.

// Fall through and Grouping cases
let a=2+2;

switch(a) {
    case 3:
        console.log("three");
    case 4:
        console.log("four"); // no break - the control falls through
    case 2+2+1:   // expression can be given as case 
        console.log("five");
    case 7:  // grouping cases 
    case 8:
    case 9:
        console.log("nine");
    default:
        console.log("default"); // even default executed
}

Case 2: Comparison is always strict.

// comaparision is always strict 
let b="4";

switch(b) {  // not converted to number
    case 4:
        console.log("number : 4");
        break;
    case "4":  
        console.log("string :4") ;  // output 
        break;
    default:
        console.log("default");
}

Case 3: Instruction in case clause. The case clause is executed but statements inside the case clause are not executed.

let c="4";
switch(c) { // all case executes , not the statements inside 
        case console.log("JS"):
            console.log("JS2");
        case console.log("Py"):
            console.log("Py2");
        default:
            console.log("Cpp"); // executed

}

Complete Code Listing

let a=2+2;

switch(a) {
    case 3:
        console.log("three");
    case 4:
        console.log("four"); // no break - the control falls through
    case 2+2+1:   // expression can be given as case 
        console.log("five");
    case 7:  // grouping cases 
    case 8:
    case 9:
        console.log("nine");
    default:
        console.log("default"); // even default executed
}


// comaparision is always strict 
let b="4";

switch(b) {  // not converted to number
    case 4:
        console.log("number : 4");
        break;
    case "4":  
        console.log("string :4") ;  // output 
        break;
    default:
        console.log("default");
}

// Other scenarios
let c="4";
switch(c) { // all case executes , not the statements inside 
        case console.log("JS"):
            console.log("JS2");
        case console.log("Py"):
            console.log("Py2");
        default:
            console.log("Cpp");

}

// 2
c= undefined;

switch(c) { // undefined
    case undefined:
            console.log("Undefined");
            break;
    case undefined:
            console.log("Undefined2");
    default:
        console.log("default");
}

// 3
c=4;
switch(c) { // a, 4, d
    case console.log("a"), console.log(c):
        console.log("c");
    default :
        console.log("d");
}