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30secondsofcode
2019-08-11 17:27:12 +00:00
parent 506164f7cb
commit 43b75db27c
5 changed files with 12 additions and 6 deletions
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7
README.md
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@ -1366,13 +1366,14 @@ Returns the index of the last element for which the provided function returns a
Use `Array.prototype.map()` to map each element to an array with its index and value.
Use `Array.prototype.filter()` to remove elements for which `fn` returns falsy values, `Array.prototype.pop()` to get the last one.
`-1` is the default value when not found.
```js
const findLastIndex = (arr, fn) =>
arr
(arr
.map((val, i) => [i, val])
.filter(([i, val]) => fn(val, i, arr))
.pop()[0];
.pop() || [-1])[0];
```
<details>
@ -1380,6 +1381,7 @@ const findLastIndex = (arr, fn) =>
```js
findLastIndex([1, 2, 3, 4], n => n % 2 === 1); // 2 (index of the value 3)
findLastIndex([1, 2, 3, 4], n => n === 5); // -1 (default value when not found)
```
</details>
@ -4818,6 +4820,7 @@ const checkProp = (predicate, prop) => obj => !!predicate(obj[prop]);
const lengthIs4 = checkProp(l => l === 4, 'length');
lengthIs4([]); // false
lengthIs4([1,2,3,4]); // true

1
docs/function.html
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@ -159,6 +159,7 @@ console<span class="token punctuation">.</span><span class="token function">log<
<span class="token keyword">const</span> lengthIs4 <span class="token operator">=</span> <span class="token function">checkProp</span><span class="token punctuation">(</span>l <span class="token operator">=></span> l <span class="token operator">===</span> <span class="token number">4</span><span class="token punctuation">,</span> <span class="token string">'length'</span><span class="token punctuation">);</span>
<span class="token function">lengthIs4</span><span class="token punctuation">([]);</span> <span class="token comment">// false</span>
<span class="token function">lengthIs4</span><span class="token punctuation">([</span><span class="token number">1</span><span class="token punctuation">,</span><span class="token number">2</span><span class="token punctuation">,</span><span class="token number">3</span><span class="token punctuation">,</span><span class="token number">4</span><span class="token punctuation">]);</span> <span class="token comment">// true</span>

7
docs/index.html
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@ -185,12 +185,13 @@
<span class="token punctuation">);</span> <span class="token comment">// [ { id: 2, value: 'c' } ]</span>
</pre></div><div class="card code-card"><div class="corner beginner" aria-label="beginner" title="beginner"></div><div class="section card-content"><h4 id="findlast">findLast</h4><p>Returns the last element for which the provided function returns a truthy value.</p><p>Use <code>Array.prototype.filter()</code> to remove elements for which <code>fn</code> returns falsy values, <code>Array.prototype.pop()</code> to get the last one.</p></div><div class="copy-button-container"><button class="copy-button" aria-label="Copy to clipboard"></button></div><pre class="section card-code language-js"><span class="token keyword">const</span> <span class="token function-variable function">findLast</span> <span class="token operator">=</span> <span class="token punctuation">(</span>arr<span class="token punctuation">,</span> fn<span class="token punctuation">)</span> <span class="token operator">=></span> arr<span class="token punctuation">.</span><span class="token function">filter</span><span class="token punctuation">(</span>fn<span class="token punctuation">).</span><span class="token function">pop</span><span class="token punctuation">();</span>
</pre><label class="collapse">examples</label><pre class="section card-examples language-js"><span class="token function">findLast</span><span class="token punctuation">([</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">],</span> n <span class="token operator">=></span> n <span class="token operator">%</span> <span class="token number">2</span> <span class="token operator">===</span> <span class="token number">1</span><span class="token punctuation">);</span> <span class="token comment">// 3</span>
</pre></div><div class="card code-card"><div class="corner intermediate" aria-label="intermediate" title="intermediate"></div><div class="section card-content"><h4 id="findlastindex">findLastIndex</h4><p>Returns the index of the last element for which the provided function returns a truthy value.</p><p>Use <code>Array.prototype.map()</code> to map each element to an array with its index and value. Use <code>Array.prototype.filter()</code> to remove elements for which <code>fn</code> returns falsy values, <code>Array.prototype.pop()</code> to get the last one.</p></div><div class="copy-button-container"><button class="copy-button" aria-label="Copy to clipboard"></button></div><pre class="section card-code language-js"><span class="token keyword">const</span> <span class="token function-variable function">findLastIndex</span> <span class="token operator">=</span> <span class="token punctuation">(</span>arr<span class="token punctuation">,</span> fn<span class="token punctuation">)</span> <span class="token operator">=></span>
arr
</pre></div><div class="card code-card"><div class="corner intermediate" aria-label="intermediate" title="intermediate"></div><div class="section card-content"><h4 id="findlastindex">findLastIndex</h4><p>Returns the index of the last element for which the provided function returns a truthy value.</p><p>Use <code>Array.prototype.map()</code> to map each element to an array with its index and value. Use <code>Array.prototype.filter()</code> to remove elements for which <code>fn</code> returns falsy values, <code>Array.prototype.pop()</code> to get the last one. <code>-1</code> is the default value when not found.</p></div><div class="copy-button-container"><button class="copy-button" aria-label="Copy to clipboard"></button></div><pre class="section card-code language-js"><span class="token keyword">const</span> <span class="token function-variable function">findLastIndex</span> <span class="token operator">=</span> <span class="token punctuation">(</span>arr<span class="token punctuation">,</span> fn<span class="token punctuation">)</span> <span class="token operator">=></span>
<span class="token punctuation">(</span>arr
<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">((</span>val<span class="token punctuation">,</span> i<span class="token punctuation">)</span> <span class="token operator">=></span> <span class="token punctuation">[</span>i<span class="token punctuation">,</span> val<span class="token punctuation">])
.</span><span class="token function">filter</span><span class="token punctuation">(([</span>i<span class="token punctuation">,</span> val<span class="token punctuation">])</span> <span class="token operator">=></span> <span class="token function">fn</span><span class="token punctuation">(</span>val<span class="token punctuation">,</span> i<span class="token punctuation">,</span> arr<span class="token punctuation">))
.</span><span class="token function">pop</span><span class="token punctuation">()[</span><span class="token number">0</span><span class="token punctuation">];</span>
.</span><span class="token function">pop</span><span class="token punctuation">()</span> <span class="token operator">||</span> <span class="token punctuation">[</span><span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">])[</span><span class="token number">0</span><span class="token punctuation">];</span>
</pre><label class="collapse">examples</label><pre class="section card-examples language-js"><span class="token function">findLastIndex</span><span class="token punctuation">([</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">],</span> n <span class="token operator">=></span> n <span class="token operator">%</span> <span class="token number">2</span> <span class="token operator">===</span> <span class="token number">1</span><span class="token punctuation">);</span> <span class="token comment">// 2 (index of the value 3)</span>
<span class="token function">findLastIndex</span><span class="token punctuation">([</span><span class="token number">1</span><span class="token punctuation">,</span> <span class="token number">2</span><span class="token punctuation">,</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">],</span> n <span class="token operator">=></span> n <span class="token operator">===</span> <span class="token number">5</span><span class="token punctuation">);</span> <span class="token comment">// -1 (default value when not found)</span>
</pre></div><div class="card code-card"><div class="corner intermediate" aria-label="intermediate" title="intermediate"></div><div class="section card-content"><h4 id="flatten">flatten</h4><p>Flattens an array up to the specified depth.</p><p>Use recursion, decrementing <code>depth</code> by 1 for each level of depth. Use <code>Array.prototype.reduce()</code> and <code>Array.prototype.concat()</code> to merge elements or arrays. Base case, for <code>depth</code> equal to <code>1</code> stops recursion. Omit the second argument, <code>depth</code> to flatten only to a depth of <code>1</code> (single flatten).</p></div><div class="copy-button-container"><button class="copy-button" aria-label="Copy to clipboard"></button></div><pre class="section card-code language-js"><span class="token keyword">const</span> <span class="token function-variable function">flatten</span> <span class="token operator">=</span> <span class="token punctuation">(</span>arr<span class="token punctuation">,</span> depth <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">)</span> <span class="token operator">=></span>
arr<span class="token punctuation">.</span><span class="token function">reduce</span><span class="token punctuation">((</span>a<span class="token punctuation">,</span> v<span class="token punctuation">)</span> <span class="token operator">=></span> a<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>depth <span class="token operator">></span> <span class="token number">1</span> <span class="token operator">&amp;&amp;</span> Array<span class="token punctuation">.</span><span class="token function">isArray</span><span class="token punctuation">(</span>v<span class="token punctuation">)</span> <span class="token operator">?</span> <span class="token function">flatten</span><span class="token punctuation">(</span>v<span class="token punctuation">,</span> depth <span class="token operator">-</span> <span class="token number">1</span><span class="token punctuation">) :</span> v<span class="token punctuation">), []);</span>
</pre><label class="collapse">examples</label><pre class="section card-examples language-js"><span class="token function">flatten</span><span class="token punctuation">([</span><span class="token number">1</span><span class="token punctuation">, [</span><span class="token number">2</span><span class="token punctuation">],</span> <span class="token number">3</span><span class="token punctuation">,</span> <span class="token number">4</span><span class="token punctuation">]);</span> <span class="token comment">// [1, 2, 3, 4]</span>

1
snippets/checkProp.md
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@ -24,6 +24,7 @@ const checkProp = (predicate, prop) => obj => !!predicate(obj[prop]);
const lengthIs4 = checkProp(l => l === 4, 'length');
lengthIs4([]); // false
lengthIs4([1,2,3,4]); // true