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    Optimize Expensive Computations in Recompose

    Tim KindbergTim Kindberg

    Learn how to use the 'withPropsOnChange' higher order component to help ensure that expensive prop computations are only executed when necessary. Simply specify which props are “expensive” and provide a factory function for those props.



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    00:00 I have a Fibonacci component. It displays a computation result depending on the depth passed in. I have a little example app where I can change the depth or the size or the color of my component.

    00:14 Every time a prop changed, whether it was depth, size or color, the Fibonacci was computed. I'd rather not compute this result every time a prop changed. I'd like to change this so it just gets the result and displays it directly.

    00:29 I'm going to do the work in a new higher order component called LazyResult(). LazyResult is going to make use of the width props onChange higher-order component from Recompose. It takes in two params.

    00:50 The first param is an array of prop names that we want to wait for changes in. We only want to recalculate the result when the depth changes. The next param is a prop creator. It takes in the owner props, and it has to return a prop object to merge with the owner props.

    01:11 We'll take in the depth, and we'll return a result that contains the Fibonacci computation. When I refresh, we'll see the computed number change every time I change the depth. Now, when I change the size or the color, the computed number doesn't go up.