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The logical operator AND
We have almost finished setting up filtering on the news site: When a user selects a category from the list, only news from this category is displayed on the page. But if you select the “All News” option, then all the categories disappear.
Let’s figure out why this happens. Each news category has the same filter value. But there are only four categories, the filter has five possible values. If the “All News” option is selected, then the filter value becomes 'all'. There is no news on the page with this data-category attribute value. Therefore, checking for an inequality always returns true. As a result, the hidden class is added to all news items, and they disappear from the page.
// When the filter value is 'all', the check always returns true
if (article.dataset.category !== filter.value) {
article.classList.add('hidden');
}How can we tell JavaScript that if the “All News” option is selected, then it should not hide the news? Add another condition to the if statement: the filter value should not be equal to 'all'.
// If the category IS NOT equal to the filter AND the filter is NOT equal to "All News"
if (article.dataset.category !== filter.value && filter.value !== 'all') {
article.classList.add('hidden');
}The double ampersand && is used in JavaScript to designate the logical operator AND. It allows you to combine two parts of the condition.
Let’s take a look at how it works. The strict inequality operators in our condition compare values and return true orfalse. If at least one of the operators returns false, then thanks to the logical operator AND the condition will also be considered false as a whole:
true && true; // Result: true
true && false; // Result: false
false && true; // Result: false
false && false; // Result: falseAs a result, the hidden class is added to the news story only if both checks for inequality return true.
Let’s refine our filtering. Add a check to the condition that checks whether the filter value is not strictly equal to 'all', and use the logical operator AND to combine the two parts of the condition. After that, make sure that everything works correctly.
Javascript also has the logical operator OR. It is indicated by two vertical bars and returns true if at least one of the operands returns true:
true || true; // Result: true
true || false; // Result: true
false || true; // Result: true
false || false; // Result: falseFiles
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<time datetime="2020-03-24">March 24, 2020</time>
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<time datetime="2020-03-19">February 19, 2020</time>
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<h3>Augment your reality</h3>
<p>The editors of Flashnews! have prepared a gift for their subscribers…</p>
<span class="news-tag">#Games</span>
<time datetime="2020-02-18">February 18, 2020</time>
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<time datetime="2019-12-22">December 22, 2019</time>
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<p>Studies show that if you do more, you can actually get more done.</p>
<span class="news-tag">#HR</span>
<time datetime="2019-10-12">October 12, 2019</time>
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<h3>A quadcopter is not just a fancy toy</h3>
<p>Controlling the quadcopter allows you to develop agility, spatial thinking, and the ability to climb trees…
</p>
<span class="news-tag">#Games</span>
<time datetime="2019-11-21">November 21, 2019</time>
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<h3>Infinite loops: It’s time to end them</h3>
<p>British scientists have discovered that the ability of software to function directly depends on the presence of infinite loops in it.</p>
<span class="news-tag">#IT</span>
<time datetime="2019-10-16">October 16, 2019</time>
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<h3>What shocking news! It’s so scandalous! Such a sensation!</h3>
<p>It turns out that you don’t have to be a cat to start programming in JavaScript!</p>
<span class="news-tag">#Kitties</span>
<time datetime="2019-12-22">December 22, 2019</time>
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<article class="news-block" data-category="IT">
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<h3>New graphics library</h3>
<p>Now you can create a dashboard in just a matter of seconds.</p>
<span class="news-tag">#IT</span>
<time datetime="2019-10-14">October 14, 2019</time>
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<h3>This just in: SHOCKING NEWS! Secret photos from the cat nursery</h3>
<p>No one expected that THIS was going on behind the closed doors…</p>
<span class="news-tag">#Kitties</span>
<time datetime="2019-10-13">October 13, 2019</time>
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Thanks! We’ll fix everything at once!
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- On line 6, add a check to the condition that checks whether the selected filter value is strictly unequal to
'all'. Use the logical operator AND to combine the two parts of the condition. - In the mini-browser, change the filter value first to “Kitties” and then to “All News.”
Pay attention to how the filter now works correctly.
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