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101 lines
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101 lines
5.7 KiB
Markdown
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---
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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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layout: post
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guid: https://brandonrozek.com/?p=344
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permalink: /2015/10/javascript-conditional-statements/
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kind:
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- article
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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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### <a href="#if-statement" name="if-statement"></a>If Statement {#if-statement}
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To run a block of code when a condition is true, use an <code class="language-javascript">if</code> statement.
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<pre><code class="language-javascript"> if (condition) {
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doSomething();
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}
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</code></pre>
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You can also run a block of code when a condition is false using the <code class="language-javascript">else</code> statement.
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<pre><code class="language-javascript"> 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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</code></pre>
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### <a href="#switch-statement" name="switch-statement"></a>Switch statement {#switch-statement}
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If you want to check a variable for **equality** against multiple different cases, use a <code class="language-javascript">switch</code> statement.
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<pre><code class="language-javascript"> 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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</code></pre>
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The default statement runs when the variable doesn’t equal any of the cases.
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### <a href="#while-loop" name="while-loop"></a>While loop {#while-loop}
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To run a block of code over and over again until a condition is false, use a <code class="language-javascript">while</code> loop.
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<pre><code class="language-javascript"> while (condition) {
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doSomething();
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}
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</code></pre>
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Don’t forget to include something in the loop that will eventually make the condition <code class="language-javascript">false</code>, 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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### <a href="#for-loop" name="for-loop"></a>For loop {#for-loop}
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If you want to run something a certain amount of times, use a “<code class="language-javascript">for"</code> 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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<pre><code class="language-javascript"> for (var i = 0; i < 5; i++) {
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doSomething();
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}
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</code></pre>
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Here you have the initiating statement of <code class="language-javascript">var i = 0</code>. From there you check, is <code class="language-javascript">i</code> less than 5? Yes, so then we <code class="language-javascript">doSomething();</code>. After we <code class="language-javascript">doSomething();</code>, we add 1 to <code class="language-javascript">i</code>. Now <code class="language-javascript">i</code> equals 2. Is <code class="language-javascript">i</code> still less than 5? Yes, so we <code class="language-javascript">doSomething();</code>. Then we add 1 to <code class="language-javascript">i</code> again. This loop will keep happening until <code class="language-javascript">i</code> is not less than 5.
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### <a href="#conclusion" name="conclusion"></a>Conclusion {#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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<pre><code class="language-javascript"> 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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</code></pre>
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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).
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