What does props.plugs.length mean in this case?

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Java

I am running into an issue where the first if statement is true and returns the "No plug available. I am not sure what props.plugs.length means and/or where to look to fix this.

window.PlugsView = function (props) {
	if (props.plugs.length == 0)
		return (<div>No plug available.</div>);

	var rows = props.plugs.map(function (plug) {
		return (
			<PlugCard key={plug.name}
				plug={plug} />);
	});

	return (
		<div>
			{rows}
		</div>);
}

What I have tried:

Have not tried much, not sure where to start.