Function that creates a rainbow clock on element given its ID

clock.js

var createTimeUpdater = function (clockId){
    var clockElement = document.getElementById(clockId);

    var rainbowColors = [
        "#FF0000",
        "#FF7F00",
        "#FFFF00",
        "#00FF00",
        "#0000FF",
        "#2E2B5F",
        "#8B00FF"
    ];

    var index = 0;

    return function(){
        clockElement.innerText = (new Date()).toLocaleTimeString();
        clockElement.style.color = rainbowColors[index];
        index= (index + 1) % rainbowColors.length;
    };
};

setInterval(createTimeUpdater("clock"), 1000);