html+js 纯前端字母或汉字头像生成插件偶然发现码云上有个非常人性化的细节：会自动给没头像的用户生成一个昵称首字符的彩色头像，关键是打开控制台一看，发现这头像居然还是在前端实时生成的这就很有意思了!
以前知道 WordPress 有一款插件WP First Letter Avatar能实现类似的功能，但采用的是 php 在后端生成头像，使用起来不是很灵活。
仔细研究了码云的前端代码，发现它使用的是一个叫LetterAvatar的 JS 插件。它的原理是利用动态创建的 canvas 生成图像，然后显示在 img 标签中。具体的代码以及调用示例可以直接看下面的在线演示：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="renderer" content="webkit">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
<title>名字头像生成实例</title>
<style>
* {
font-family: microsoft yahei;
font-family: "Exo 2", "iconfont", "Trebuchet MS", "Helvetica", "Arial", 'PingFang SC', 'Hiragino Sans GB', 'STHeiti Light', 'Microsoft YaHei', 'SimHei', 'WenQuanYi Micro Hei', sans-serif;
letter-spacing: 0.04em;
}
.container {
max-width: 1000px;
}
h3 {
margin-top: 35px;
margin-bottom: 20px;
}
.round { border-radius: 50%; }
</style>
</head>
<body>
<h3>使用方法</h3>
<pre>
<code><img width="256" height="256" avatar="Ban Xian" color="#0D8ABC"></code>
</pre>
<h3>在线演示</h3>
<img width="256" height="256" avatar="Ban Xian" color="#0D8ABC">
<div>
<img width="100" height="100" avatar="默">
<img width="100" height="100" avatar="认">
<img width="100" height="100" avatar="头" color="#2c3e50">
<img width="100" height="100" avatar="像" color="#c0392b">
</div>
<br>
<div>
<img class="round" width="100" height="100" avatar="内蒙古">
<img class="round" width="100" height="100" avatar="角">
<img class="round" width="100" height="100" avatar="示" color="#e67e22">
<img class="round" width="100" height="100" avatar="例" color="#0092de">
</div>
<script>
(function(w, d){
function LetterAvatar (name, size, color) {
name = name || '';
size = size || 60;
var colours = [
"#1abc9c", "#2ecc71", "#3498db", "#9b59b6", "#34495e", "#16a085", "#27ae60", "#2980b9", "#8e44ad", "#2c3e50",
"#f1c40f", "#e67e22", "#e74c3c", "#00bcd4", "#95a5a6", "#f39c12", "#d35400", "#c0392b", "#bdc3c7", "#7f8c8d"
],
nameSplit = String(name).split(' '),
initials, charIndex, colourIndex, canvas, context, dataURI;
if (nameSplit.length == 1) {
initials = nameSplit[0] ? nameSplit[0].charAt(0):'?';
} else {
initials = nameSplit[0].charAt(0) + nameSplit[1].charAt(0);
}
if (w.devicePixelRatio) {
size = (size * w.devicePixelRatio);
}
charIndex = (initials == '?' ? 72 : initials.charCodeAt(0)) - 64;
colourIndex = charIndex % 20;
canvas = d.createElement('canvas');
canvas.width = size;
canvas.height = size;
context = canvas.getContext("2d");
context.fillStyle = color ? color : colours[colourIndex - 1];
context.fillRect (0, 0, canvas.width, canvas.height);
context.font = Math.round(canvas.width/2)+"px 'Microsoft Yahei'";
context.textAlign = "center";
context.fillStyle = "#FFF";
context.fillText(initials, size / 2, size / 1.5);
dataURI = canvas.toDataURL();
canvas = null;
return dataURI;
};
LetterAvatar.transform = function() {
Array.prototype.forEach.call(d.querySelectorAll('img[avatar]'), function(img, name, color) {
name = img.getAttribute('avatar');
color = img.getAttribute('color');
img.src = LetterAvatar(name, img.getAttribute('width'), color);
img.removeAttribute('avatar');
img.setAttribute('alt', name);
});
};
// AMD support
if (typeof define === 'function' && define.amd) {
define(function () { return LetterAvatar; });
// CommonJS and Node.js module support.
} else if (typeof exports !== 'undefined') {
// Support Node.js specific `module.exports` (which can be a function)
if (typeof module != 'undefined' && module.exports) {
exports = module.exports = LetterAvatar;
}
// But always support CommonJS module 1.1.1 spec (`exports` cannot be a function)
exports.LetterAvatar = LetterAvatar;
} else {
window.LetterAvatar = LetterAvatar;
d.addEventListener('DOMContentLoaded', function(event) {
LetterAvatar.transform();
});
}
})(window, document);
</script>
</body>
</html>
