Intercept example

intercept.js

const theme = observable({
	backgroundColor: "#ffffff"
})

intercept(theme, "backgroundColor", change => {
	if (!change.newValue) {
		// ignore attempts to unset the background color
		return null;   
	}
	if (change.newValue.length === 6) {
		// correct missing '#' prefix
		change.newValue = '#' + change.newValue;
		return change;   
	}
	if (change.newValue.length === 7) {
		// this must be a properly formatted color code!
		return change;
	}
	throw new Error("This doesn't look like a color at all: " + change.newValue);
})

theme.backgroundColor = "acacac" // will become #acacac