JavaScript: Branch Control: if then else, switch

If Statement

Simple “if” statement syntax:

if (testExpr) {body}

The curly brackets {} are optional when there is only one statement or expression in body.

If testExpr is true, run body, else do nothing.

The testExpr is forced into one of true or false by Boolean Constructor.

if (3 < 4) {
  console.log("yes");
  console.log("and yes");
}

if (3 < 4) console.log("yes");

If-Else Statement

• if (testExpr) {trueBody} else {falseBody}

if (3 <= 4) console.log("yes");
else console.log("no");

“else if” chain.

const x = 3;
if (x == 1) console.log("is 1");
else if (x == 2) console.log("is 2");
else if (x == 3) console.log("is 3");
else console.log("not found");

If-Then-Else Expression

testExpr ? expr1 : expr2

if testExpr eval to true, then return expression expr1, else return expr2.

console.log(((4 > 5) ? "yes" : "no") === "no");

Switch Statement

// example of switch statement

const x = "a";

switch (x) {
  case "w":
    console.log("is w");
    break; // without “break”, it'll continue to run rest without testing
  case "a":
    console.log("is a");
    break;
  case 3:
    console.log("is 3");
    break;
  default:
    console.log("none of the above");
}

Switch-statement uses the Triple Equal Operator to test equality.