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) {
  // something
  console.log("yes");
}

If-Else Statement

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

if (3 <= 4) {
  // something
  console.log("yes");
} else {
  // something
  console.log("no");
}

Else-If Chain

const x = 3;
if (x == 1) {
  // something
  console.log("is 1");
} else if (x == 2) {
  // something
  console.log("is 2");
} else if (x == 3) {
  // something
  console.log("is 3");
} else {
  // something
  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

The switch statement compares a value to a sequence of values, one by one.

Tip: switch is not useful. It is not a replacement for if-else chain, because it only compares a value, you cannot give it a general true/false expression.

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

// 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");
}