反转元素颜色的功能。获取每个的亮度，如果它们接近，则反转文本颜色。
function adjustColor(element) {
var style = window.getComputedStyle(element);
var background = new Color(style['background-color']);
var text = new Color(style['color']);
if (Math.abs(background.luma - text.luma) < 100) {
element.style.color = text.inverted.toString();
}
}
下面的颜色“类”。接受 hex、rgb、rgba（即使是百分比），也可以输出到任何一个。 Explorer 需要为 String.padStart 和 String.startsWith 使用 polyfill，并且需要使用 concat 修改 toString() 方法中的插值字符串。
const Color = (function () {
function toHex(num, padding) { return num.toString(16).padStart(padding || 2); }
function parsePart(value) {
var perc = value.lastIndexOf('%');
return perc < 0 ? value : value.substr(0, perc);
}
function Color(data) {
if (arguments.length > 1) {
this[0] = arguments[0];
this[1] = arguments[1];
this[2] = arguments[2];
if (arguments.length > 3) { this[3] = arguments[3]; }
} else if (data instanceof Color || Array.isArray(data)) {
this[0] = data[0];
this[1] = data[1];
this[2] = data[2];
this[3] = data[3];
} else if (typeof data === 'string') {
data = data.trim();
if (data[0] === "#") {
switch (data.length) {
case 4:
this[0] = parseInt(data[1], 16); this[0] = (this[0] << 4) | this[0];
this[1] = parseInt(data[2], 16); this[1] = (this[1] << 4) | this[1];
this[2] = parseInt(data[3], 16); this[2] = (this[2] << 4) | this[2];
break;
case 9:
this[3] = parseInt(data.substr(7, 2), 16);
//Fall Through
case 7:
this[0] = parseInt(data.substr(1, 2), 16);
this[1] = parseInt(data.substr(3, 2), 16);
this[2] = parseInt(data.substr(5, 2), 16);
break;
}
} else if (data.startsWith("rgb")) {
var parts = data.substr(data[3] === "a" ? 5 : 4, data.length - (data[3] === "a" ? 6 : 5)).split(',');
this.r = parsePart(parts[0]);
this.g = parsePart(parts[1]);
this.b = parsePart(parts[2]);
if (parts.length > 3) { this.a = parsePart(parts[3]); }
}
}
}
Color.prototype = {
constructor: Color,
0: 255,
1: 255,
2: 255,
3: 255,
get r() { return this[0]; },
set r(value) { this[0] = value == null ? 0 : Math.max(Math.min(parseInt(value), 255), 0); },
get g() { return this[1]; },
set g(value) { this[1] = value == null ? 0 : Math.max(Math.min(parseInt(value), 255), 0); },
get b() { return this[2]; },
set b(value) { this[2] = value == null ? 0 : Math.max(Math.min(parseInt(value), 255), 0); },
get a() { return this[3] / 255; },
set a(value) { this[3] = value == null ? 255 : Math.max(Math.min(value > 1 ? value : parseFloat(value) * 255, 255), 0); },
get luma() { return .299 * this.r + .587 * this.g + .114 * this.b; },
get inverted() { return new Color(255 - this[0], 255 - this[1], 255 - this[2], this[3]); },
toString: function (option) {
if (option === 16) {
return '#' + toHex(this.r) + toHex(this.g) + toHex(this.b) + (this[3] === 255 ? '' : toHex(this[3]));
} else if (option === '%') {
if (this.a !== 1) {
return `rgba(${this.r / 255 * 100}%, ${this.b / 255 * 100}%, ${this.g / 255 * 100}%, ${this.a / 255})`;
} else {
return `rgb(${this.r / 255 * 100}%, ${this.b / 255 * 100}%, ${this.g / 255 * 100})%`;
}
} else {
if (this.a !== 1) {
return `rgba(${this.r}, ${this.b}, ${this.g}, ${this.a})`;
} else {
return `rgb(${this.r}, ${this.b}, ${this.g})`;
}
}
}
};
return Color;
}());