TypeScript hasDuplicates Example

TypeScript function that indicates if a strongly typed TypeScript array contains duplicates.

by Matthew Heironimus

HTML

<div style="background: #272822; overflow:auto;width:auto;border:solid gray;border-width:.1em .1em .1em .8em;padding:.2em .6em;"><pre style="margin: 0; line-height: 125%"><span style="color: #66d9ef">const</span> <span style="color: #a6e22e">uniqueArray</span>: <span style="color: #66d9ef">string</span><span style="color: #f8f8f2">[]</span> <span style="color: #f92672">=</span> <span style="color: #f8f8f2">[</span><span style="color: #e6db74">&quot;one&quot;</span><span style="color: #f8f8f2">,</span> <span style="color: #e6db74">&quot;two&quot;</span><span style="color: #f8f8f2">,</span> <span style="color: #e6db74">&quot;three&quot;</span><span style="color: #f8f8f2">];</span>
<span style="color: #a6e22e">hasDuplicates</span><span style="color: #f8f8f2">(</span><span style="color: #a6e22e">uniqueArray</span><span style="color: #f8f8f2">);</span>
</pre></div>

<code>
hasDuplicates(uniqueArray): <span id="uniqueArrayResult"></span>
</code>

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<!-- HTML generated using hilite.me --><div style="background: #272822; overflow:auto;width:auto;border:solid gray;border-width:.1em .1em .1em .8em;padding:.2em .6em;"><pre style="margin: 0; line-height: 125%"><span style="color: #66d9ef">const</span> <span style="color: #a6e22e">duplicateArray</span>: <span style="color: #66d9ef">number</span><span style="color: #f8f8f2">[]</span> <span style="color: #f92672">=</span> <span style="color: #f8f8f2">[</span><span style="color: #ae81ff">1</span><span style="color: #f8f8f2">,</span> <span style="color: #ae81ff">2</span><span style="color: #f8f8f2">,</span> <span style="color: #ae81ff">1</span><span style="color: #f8f8f2">];</span>
<span style="color: #a6e22e">hasDuplicates</span><span style="color: #f8f8f2">(</span><span style="color: #a6e22e">duplicateArray</span><span style="color: #f8f8f2">);</span>
</pre></div>


<code>
hasDuplicates(duplicateArray): <span id="duplicateArrayResult"></span>
</code>

TypeScript

function hasDuplicates<T>(inputArray: T[]): boolean {
    return inputArray.length !== (new Set(inputArray)).size;
}

const uniqueArray: string[] = ["one", "two", "three"];
$("#uniqueArrayResult").text(hasDuplicates(uniqueArray));


const duplicateArray: number[] = [1, 2, 1];
$("#duplicateArrayResult").text(hasDuplicates(duplicateArray));