James Garbutt

Software engineer. Front-end @crispthinking. JavaScript & HTML5 expert.

Thoughts on JavaScript's spread operators

May 27, 2017

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Just a quick thought…

The spread operator is a cool little thing, it looks like this:

const foo = {
    "a": 1,
    "b": 2
};

const bar = { ...foo, "c": 3 };

Where supported, it comes in useful for many things, such as the ability to concatenate and copy arrays/objects with ease.

Pass all the things!

I recently converted a React project to use TypeScript, it was all going great until this snippet:

render() {
    return <Foo {...this.props} />;
}

This simple line threw a bunch of compilation errors. Why? Well, Foo doesn’t have the same properties as this. The two components are hugely different, with Foo sharing only one or two properties in fact.

So, we were originally relying on the fact that some of the properties did match up and it was enough for the application to work correctly.

I would much rather have the more verbose code:

render() {
    return (<Foo
        x={this.props.x}
        y={this.props.y}
        z={this.props.z}
    />);
}

You can quickly see exactly what is being passed to Foo and where from. Whereas with the old code, it was far from clear what it contains without looking through the props.

Thoughts?

Be careful with your props, guys!

You should totally give TypeScript a go if you haven’t already, too. I would highly recommend you check it out. I would have never noticed this lazy piece of code if not for the great type checking and inference.

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