img转base64

img转base64

一个简单的img地址转base64格式，并可以设置压缩比例以及图片格式

// 参数说明：图片地址（本地或者线上url）、处理后返回的base64内容、指定图片类型
function imgToBase64(url, outputFormat) {
    
	return new Promise((resolve, reject) => {
    
		const canvas = document.createElement('canvas');
		const ctx = canvas.getContext('2d');
		const img = new Image;
		img.crossOrigin = 'Anonymous';	//解决Canvas.toDataURL 图片跨域问题
		img.onload = () => {
    
			let width = img.width;
			let height = img.height;
			
			// 压缩比例 -- 可以自己修改参数。500px宽度以下原尺寸，大于500px比例处理
			let bili = Math.round(width / 500) || 1;
			let rate = 1 / bili;
			canvas.width = width * rate;
			canvas.height = height * rate;
			ctx.drawImage(img, 0, 0, width, height, 0, 0, width * rate, height * rate);
			let dataURL = canvas.toDataURL(outputFormat || 'image/jpeg');
			// 去除标头 -- 传递给后台时一般去除头部
			// let reg = new RegExp('^data:image/[^;]+;base64,');
			// dataURL = dataURL.replace(reg, '');
			canvas = null;
			resolve(dataURL);
		}
		img.src = url;
	})
};

// 调用：
imgToBase64("https://img0.bdstatic.com/static/searchdetail/img/logo-2X_2dd9a28.png").then(res => console.log(res))