Map, Filter and Reduce – Animated

Map, filter and reduce have been around for a long time. They are often seen as part of Functional Programming style.

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Here’s a list of my best web development tutorials.

Complete CSS flex tutorial on Hashnode.

Ultimate CSS grid tutorial on Hashnode.

Higher-order functions .map, .filter & .reduce on Hashnode.

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We often commit complex ideas to memory by visualizing them. There aren’t many coding articles using visuals as starting point for learning. And yet, visualization plays important role in education. This also applies to coding.

Even after working with map, filter and reduce for years I still often find myself asking: Is a copy of the original array made? Is reference to the original array modified? I made this tutorial to put an end to these questions.

My hope is that once it is seen visually – it will be easier to memorize. map all values to an expression. apply “value + 1” to a set of 7 numbers [1, 2, 3, 4, 5, 6, 7]

1] Expression value + 1 is applied to every item in the original array.

2] .map() returns a modified copy of the array leaving original untouched.

3] Result: [2,3,4,5,6,7,8] (a copy of the original array is created.)

Array.filter keep all that match a condition.

NOTE: there is a small mistake in the animation. It should return [6,7], not [6,7,8]. I’ll fix it shortly. . .

1] function value > 5 is applied to every item in the original array.



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