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4.4 KiB
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103 lines
No EOL
4.4 KiB
Markdown
---
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id: 344
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title: Javascript Conditional Statements
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date: 2015-10-18T18:30:21+00:00
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author: Brandon Rozek
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aliases:
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- /2015/10/javascript-conditional-statements/
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permalink: /2015/10/javascript-conditional-statements/
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tags: ["Web", "JS"]
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---
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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.
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<!--more-->
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This post is part of my lecture series for Math I/O. There is no pre-reading for this lecture.
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### If Statement
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To run a block of code when a condition is true, use an `if` statement.
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```javascript
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if (condition) {
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doSomething();
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}
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```
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You can also run a block of code when a condition is false using the `else` statement.
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```javascript
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if (condition) {
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doSomething();
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} else {
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doSomethingElse();
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}
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```
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### Switch statement
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If you want to check a variable for **equality** against multiple different cases, use a `switch` statement.
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```javascript
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switch (variable) {
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case condition1:
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doSomething();
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break;
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case condition2:
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doSomethingElse();
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break;
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default:
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doSomethingCompletelyDifferent();
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break;
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}
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```
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The default statement runs when the variable doesn’t equal any of the cases.
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### While loop
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To run a block of code over and over again until a condition is false, use a `while` loop.
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```javascript
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while (condition) {
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doSomething();
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}
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```
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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)
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### For loop
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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.
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```javascript
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for (var i = 0; i < 5; i++) {
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doSomething();
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}
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```
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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.
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### Conclusion
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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.
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```javascript
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if (youLikeThisPost) {
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console.log("Come back next week! :)");
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} else {
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console.log("Aww that's okay, you should give me another chance next week :)");
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}
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```
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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](http://webcheatsheet.com/javascript/if_else_switch.php). |