1、FileReader
通过XMLHttpRequest请求图片Blob数据格式，然后利用FileReader转换为dataURL
function toDataURL(url, callback) {
var xhr = new XMLHttpRequest();
xhr.onload = function() {
var reader = new FileReader();
reader.onloadend = function() {
callback(reader.result);
}
reader.readAsDataURL(xhr.response);
};
xhr.open('GET', url);
xhr.responseType = 'blob';
xhr.send();
}
toDataURL('https://www.gravatar.com/avatar/d50c83cc0c6523b4d3f6085295c953e0', function(dataUrl) {
console.log('RESULT:', dataUrl)
})
请求可以利用 WHATWG fetchJs来实现
const toDataURL = url => fetch(url)
.then(response => response.blob())
.then(blob => new Promise((resolve, reject) => {
const reader = new FileReader()
reader.onloadend = () => resolve(reader.result)
reader.onerror = reject
reader.readAsDataURL(blob)
})) toDataURL('https://www.gravatar.com/avatar/d50c83cc0c6523b4d3f6085295c953e0').then(dataUrl => {
console.log('RESULT:', dataUrl)
})
优缺点：
- 某些浏览器缺乏支持
- 更好的文件压缩
- 适用其他文件类型
查看支持：
2、Canvas
新建图片，在画布上实现，然后将canvas对象转变为一个dataURL
function toDataURL(src, callback, outputFormat) {
var img = new Image();
img.crossOrigin = 'Anonymous'; // 允许image请求的图片应用到canvas，就像他们在同一个域
img.onload = function() {
var canvas = document.createElement('CANVAS');
var ctx = canvas.getContext('2d');
var dataURL;
canvas.height = this.naturalHeight;
canvas.width = this.naturalWidth;
ctx.drawImage(this, 0, 0);
dataURL = canvas.toDataURL(outputFormat);
callback(dataURL);
};
img.src = src;
if (img.complete || img.complete === undefined) { // 确保对缓存的图片也触发img.onload事件
img.src = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///ywAAAAAAQABAAACAUwAOw==";
img.src = src;
}
}
toDataURL(
'https://www.gravatar.com/avatar/d50c83cc0c6523b4d3f6085295c953e0',
function(dataUrl) {
console.log('RESULT:', dataUrl)
}
)
支持的inputFormat：
-
image/png,image/jpeg,image/jpg,image/gif,image/bmp,image/tiff,image/x-icon,image/svg+xml,image/webp,image/xxx
支持的outputFormat：
-
image/png,image/jpeg,image/webp(chrome)
查看支持：
- http://caniuse.com/#feat=canvas
- IE10 (IE10 just works with same origin images)
3、从当前文件系统读取，input读取文件后，利用FileReader进行转换
function encodeImageFileAsURL(element) {
var file = element.files[0];
var reader = new FileReader();
reader.onloadend = function() {
console.log('RESULT', reader.result)
}
reader.readAsDataURL(file);
}
<input type="file" onchange="encodeImageFileAsURL(this)" />