js 顏色10進制轉化成rgba

當我們在已知一個整數如（0~256x256x256x256 之間的顏色值），想獲得關於它的3原色加一個透明度時，及alpha, red, green, blue

提取三原色

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方法一：

    function getColor(number) {
        let color = number;
        const blue = parseInt(color % 0x100, 10);
        color = color >>> 8;
        const green = parseInt(color % 0x100, 10);
        color = color >>> 8;
        const red = parseInt(color % 0x100, 10);
        const alpha = (parseInt(color >>> 8, 10) / 0xFF).toFixed(1);
        return `rgba(${red}, ${green}, ${blue}, ${alpha})`;
    }

方法二：

function getColor(number) {
    const alpha = number >> 24 & 0xff;
    const red = number >> 16 & 0xff;
    const green = number >> 8 & 0xff;
    const blue = number & 0xff;
    return `rgba(${red}, ${green}, ${blue}, ${alpha})`;
}