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function normalizeCSSHeading(oldHeading, newHeading) {
    "use strict";
    // find the difference in degrees first
    let oldH = oldHeading;
    if (oldH < 0) {
        oldH = 365 + (oldH % 365);
    }
    let newH = newHeading;
    if (newH < 0) {
        newH = 365 + (newH % 365);
    }
    let diff = newH % 365 - oldH % 365;

    // find shortest path
    if (diff < -180) {
        diff = 365 - Math.abs(diff);
    } else if (diff > 180) {
        diff = diff - 365;
    }

    return oldHeading + diff;
}

// some jasmine tests
describe('normalizeCSSHeading', function() {
    it ('should all work', function() {
        expect(normalizeCSSHeading(0, 0)).toEqual(0);
        expect(normalizeCSSHeading(0, 10)).toEqual(10);
        expect(normalizeCSSHeading(376, 10)).toEqual(375);
        expect(normalizeCSSHeading(-124, 310)).toEqual(-55);
        expect(normalizeCSSHeading(-124, -90)).toEqual(-90);
        expect(normalizeCSSHeading(1459, 6)).toEqual(1466); // 1459 % 365 = 364
        expect(normalizeCSSHeading(-30, 200)).toEqual(-165);
        expect(normalizeCSSHeading(439, -15)).toEqual(350); // 439 % 365 = 74
        expect(normalizeCSSHeading(0, -95)).toEqual(-95);
    });
});