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.
Tip: JavaScript Switch-Statement is Goto
JavaScript's switch-statement does fall-through. It'll jump to a matching point and run all of the rest of case code without testing. Think of JavaScript switch as goto.
Add
break
if you want it to exit.