Threshold scale generator, similar to D3's

thresholdScale.js

(function ( global ) {

	'use strict';

	// Threshold scale generator, similar to D3's
	// Usage:
	//
	//    scale = thresholdScale([ 0, 20, 40, 100 ], [ 'red', 'green', 'blue' ]);
	//    scale( 10 ) -> 'red'

	var thresholdScale = function ( domain, range ) {
		var d0, d1;

		if ( domain.length !== range.length + 1 ) {
			throw new Error( 'Range must have one more value than domain' );
		}

		d0 = domain[0];
		d1 = domain[ domain.length - 1 ];

		return function ( val ) {
			var i, result;

			// if value is outside domain, return undefined
			if ( val < d0 || val > d1 ) {
				return undefined;
			}

			i = 0;
			//result = domain[0];

			while ( val > domain[i] ) {
				result = range[i];
				i += 1;
			}

			return result;
		};
	};

	// export as CommonJS module...
	if ( typeof module !== 'undefined' && module.exports ) {
		module.exports = thresholdScale;
	}

	// ... or as AMD module...
	else if ( typeof define !== 'undefined' && define.amd ) {
		define( function () { return thresholdScale; });
	}

	// ... or as browser global
	else {
		global.thresholdScale = thresholdScale;
	}

}( this ));