Javascript Conditional Statements

Brandon Rozek

October 18, 2015

Javascript, like most other programming languages, include ways to run blocks of code when something meets a condition. Here, I will describe the most common ways to do so.

This post is part of my lecture series for Math I/O. There is no pre-reading for this lecture.

If Statement

To run a block of code when a condition is true, use an if statement.

    if (condition) {
        doSomething();
    }

You can also run a block of code when a condition is false using the else statement.

    if (condition) {
        doSomething();
    } else {
        doSomethingElse();
    }

Switch statement

If you want to check a variable for equality against multiple different cases, use a switch statement.

    switch (variable) {
        case condition1:
            doSomething();
            break;
        case condition2:
            doSomethingElse();
            break;
        default:
            doSomethingCompletelyDifferent();
            break;
    }

The default statement runs when the variable doesn’t equal any of the cases.

While loop

To run a block of code over and over again until a condition is false, use a while loop.

    while (condition) {
        doSomething();
    }

Don’t forget to include something in the loop that will eventually make the condition false, otherwise you run into an infinite loop. (Which is a loop that never stops repeating itself; most likely crashing your browser)

For loop

If you want to run something a certain amount of times, use a “for” loop. For loops can be broken down into three components: an initiating statement, a condition, and a statement that runs after every loop.

    for (var i = 0; i < 5; i++) {
        doSomething();
    }

Here you have the initiating statement of var i = 0. From there you check, is i less than 5? Yes, so then we doSomething();. After we doSomething();, we add 1 to i. Now i equals 2. Is i still less than 5? Yes, so we doSomething();. Then we add 1 to i again. This loop will keep happening until i is not less than 5.

Conclusion

Having different control/conditional statements helps keep the state of any application you’re making. Did the user say not to notify them? Then don’t, otherwise (else) notify them. That’s all I have to say for this week. Hope this post helps you get a little more used to this big world called programming.

    if (youLikeThisPost) {
        console.log("Come back next week! :)");
    } else {
        console.log("Aww that's okay, you should give me another chance next week :)");
    }

I recommend that you look at different perspectives of the same concepts. WebCheatSheet.com has a similar post to mine, check out what they had to say here.