The if statement executes some code if a specified condition is true.
if (true) {
console.log("this will be printed");
}
if (false) {
console.log("this will not be printed");
}
var x = 4;
//var x = 5;
if (x === 5) {
console.log("x equals 5");
}
if/else
When we want code that executes when the if statement condition is false, we can use the else keyword as a shorthand.
var isTasty;
var food = "vegetables";
//var food = "pizza";
if (food === "pizza") {
isTasty = true;
} else {
isTasty = false;
}
console.log("Is the food tasty?", isTasty);
if/else if/else
var course = "wdi";
if (course === "uxdi") {
console.log("Hello, User Experience Designer!");
} else if (course === "fewd") {
console.log("Hello, Front-End Developer");
} else if (course === "wdi") {
console.log("Hello, Immersed Developer")
} else {
console.log("Who are you?")
}
switch
Sometimes, numerous if/else statements make code hard to read. There's an alternative called a switch statement. It accepts a value and compares the value against various cases.
Each case block must end with break;, otherwise the block will fall through to the next block. If none of the cases match the value, you can also implement a default case.
var grade = "B";
switch(grade) {
case "A":
console.log('You got an A! Great job!');
break;
case "B":
console.log('You got an B! Good job!');
break;
default:
console.log('Try again next time!');
break;
}
Exercise:
Rewrite the if/else if/else example above using a switch statement.
Switch statements can evaluate inequalities too!
var grade = "75";
switch(true) {
case (90<=grade && grade<=100):
console.log('You got an A! Great job!');
break;
case (80<=grade && grade<90):
console.log('You got an B! Good job!');
break;
case (70<=grade && grade<80):
console.log('You got an C! Fair job!');
break;
default:
console.log('Try again next time!');
break;
}
Truthy vs. Falsey
What happens if we put something other than a Boolean as the conditional in an if statement? Turns out, any value can be evaluated as true or false.
Most values are truthy. In fact, there are only 6 falsey values in Javascript - can you guess them all?
var person = null;
if (person) {
console.log("this will not be printed");
} else {
console.log("this will be printed");
}
var num = 0;
if (num) {
console.log("this will not be printed");
} else {
console.log("this will be printed");
}
var num = 5;
if (num) {
console.log("this will be printed");
}