React indeterminate

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I've fallen in love with React.js and JSX over the years; state-based rendering and a logical workflow have made me see the light of this modern framework. That doesn't mean I don't sometimes get a bit frustrated that the "simple" things seem harder than they should be. Getting a reference to an element and modifying its properties used to be simple but now you have to take into account you don't usually have element references -- you need to think in a different way. I learned this when I needed to set a checkbox's inderterminate property, a property not recognized via an attribute, one that requires a handle on the element and setting a property directly.

To add the indeterminate property to the checkbox, I needed to take advantage of the ref attribute:

const { value, checked, indeterminate } = this.props

return render(
    <input
        type="checkbox"
        value={value}
        checked={checked}
        ref={el => el && (el.indeterminate = indeterminate)}
    />
)

Since the ref is run on each render, the indeterminate property is updated appropriately, and thus the checkbox appears as expected.

Regardless of how amazing your framework appears, there's always a blind spot that requires a bit of a hack to accomplish what's expected. That's what a framework does, though: gives you 99% of what you need and makes the 1% difficult!

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Discussion

  1. BryanYang

    the last words are exactly. there is always something we miss when we design a framework. so the best way is to optimize again and again.

  2. > Since the ref is run on each render, the indeterminate property is updated appropriately, and thus the checkbox appears as expected.

    This is kind of true but it’s probably not working how you imagined in your head. The ref doesn’t actually get run each render, only when the component mounts/unmounts or the function passed to ref changes.

    In your example since you’re using an anonymous function this looks like a new function every time the component re-renders and so React will call it again. If you were to replace that ref with a function that doesn’t change every render (e.g ref={ this.setCheckboxRef }, this example would no longer work.

    This is the exact scenario described in the caveats section of the docs here: https://reactjs.org/docs/refs-and-the-dom.html#caveats-with-callback-refs

    Instead you want to assign the ref to a class property and listen to prop changes in componentDidUpdate and proxy them to the checkbox (if you’re using a class component) or use the new useEffect API in hooks.

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