feat: Added percent

Author: terkelg

docs/index.html

@@ -273,6 +273,16 @@ <h3 class='mb0 no-anchor'></h3>
 
                 </li>
 
+                
+                <li><a
+                  href='#percent'
+                  class="">
+                  percent
+                  
+                </a>
+                
+                </li>
+              
             </ul>
           </div>
           <div class='mt1 h6 quiet'>
@@ -2187,6 +2197,97 @@ <h3 class='fl m0' id='iseven'>
 
 
 
+</section>
+
+          
+        
+          
+            <section class='p2 mb2 clearfix bg-white minishadow'>
+
+  
+  <div class='clearfix'>
+    <h3 class='fl m0' id='percent'>
+      percent
+    </h3>
+    
+  </div>
+  
+
+  <p>Work out what percentage value <code>a</code> is of value <code>b</code> using the given base.</p>
+
+
+  <div class='pre p1 fill-light mt0'>percent(number: integer, a: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a>, b: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a>, base: [<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a>]): <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a></div>
+
+  
+
+  
+  
+  
+  
+  
+
+  
+    <div class='py1 quiet mt1 prose-big'>Parameters</div>
+    <div class='prose'>
+      
+        <div class='space-bottom0'>
+          <div>
+            <span class='code bold'>number</span> <code class='quiet'>(integer)</code> The number to check.
+
+          </div>
+          
+        </div>
+      
+        <div class='space-bottom0'>
+          <div>
+            <span class='code bold'>a</span> <code class='quiet'>(<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a>)</code> The value to work out the percentage for.
+
+          </div>
+          
+        </div>
+      
+        <div class='space-bottom0'>
+          <div>
+            <span class='code bold'>b</span> <code class='quiet'>(<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a>)</code> The value you wish to get the percentage of.
+
+          </div>
+          
+        </div>
+      
+        <div class='space-bottom0'>
+          <div>
+            <span class='code bold'>base</span> <code class='quiet'>([<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a>]
+            (default <code>0</code>)
+            )</code> The base value.
+
+          </div>
+          
+        </div>
+      
+    </div>
+  
+
+  
+
+  
+    
+      <div class='py1 quiet mt1 prose-big'>Returns</div>
+      <code><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number">number</a></code>:
+        The percentage a is of b, between 0 and 1.
+
+      
+    
+  
+
+  
+
+  
+
+  
+
+  
+
+  
 </section>
 
 

src/math-toolbox.js

@@ -23,3 +23,5 @@ export { minSub } from './min-sub'
 export { average } from './average'
 export { isOdd } from './is-odd'
 export { isEven } from './is-even'
+export { percent } from './percent'
+// difference

src/percent.js

@@ -0,0 +1,20 @@
+/**
+ * Work out what percentage value `a` is of value `b` using the given base.
+ *
+ * @param  {integer} number - The number to check.
+ * @param  {number} a - The value to work out the percentage for.
+ * @param  {number} b - The value you wish to get the percentage of.
+ * @param  {number} [base=0] - The base value.
+ * @return {number} The percentage a is of b, between 0 and 1.
+ */
+function percent (a, b, base = 0) {
+  if (a > b || base > b) {
+    return 1
+  } else if (a < base || base > a) {
+    return 0
+  } else {
+    return (a - base) / b
+  }
+}
+
+export { percent }

test/percent.test.js

@@ -0,0 +1,15 @@
+import { percent } from '../src/math-toolbox'
+
+describe('Work out what percentage value', () => {
+  it('Expect 125 of 100 to be 1', () => {
+    expect(percent(125, 100)).toBe(1)
+  })
+
+  it('Expect 1 of 100 to in base 2 to be 0.5', () => {
+    expect(percent(1, 100, 2)).toBe(0)
+  })
+
+  it('Expect 50 of 100 to be 0.5', () => {
+    expect(percent(50, 100)).toBe(0.5)
+  })
+})