本文实例为大家分享了vue实现压缩图片预览并上传的具体代码，供大家参考，具体内容如下
主要用到filereader、canvas 以及 formdata 这三个h6的api
过程大致分为三步：
用户使用input file上传图片的时候，用filereader读取用户上传的图片数据（base64格式）
把图片数据传入img对象，然后将img绘制到canvas上，再调用canvas.toDataURL对图片进行压缩
获取到压缩后的base64格式图片数据，转成二进制塞入formdata，再通过XmlHttpRequest提交formdata。
模板：
<template> <div class="image-box"> <input type="file" accept="image/*" @change="imageHandle"> <img ref="upImg"/> </div> </template>
获取图片数据
methods: {
//监听input file的change事件
imageHandle(e) {
//**这个是必不可少的，在下面的reader.onload中this就不再指vm了**
let that = this;
let maxSize = 100 * 1024;
let files = e.srcElement.files;
if (!files.length) return; //文件长度大于0
if (!/^image\//.test(files[0].type)) return; //必须是图片才处理
if (!window.FileReader) return; //支持FileReader
//创建filereader对象
let reader = new FileReader();
reader.readAsDataURL(files[0]); //将图片转成base64格式
reader.onload = function() {
let result = this.result;
let img = new Image();
img.src = result;
let formdata = new FormData();
if (this.result.length <= maxSize) {
that.$refs.upImg.src = result; //预览图片
img = null;
//上传图片
formdata.append("image", that._upload(result, files[0].name, files[0].type));
that.$store.dispatch("uploadImage", formdata)
.then(data => {
if (data === 1) {
that.$toast("上传成功", "success");
} else if (data === -1) {
that.$toast("图片为空", "error");
} else {
that.$toast("上传失败", "error");
}
})
.catch(error => that.$toast("上传失败", "error"));
} else {
img.onload = function() {
//压缩图片
let data = that._compress(img);
//图片预览
that.$refs.upImg.src = data;
//上传图片
formdata.append("image", that._upload(data, files[0].name, files[0].type));
that.$store.dispatch("uploadImage", formdata)
.then(data => {
if (data === 1) {
that.$toast("上传成功", "success");
} else if (data === -1) {
that.$toast("图片为空", "error");
} else {
that.$toast("上传失败", "error");
}
})
.catch(error => that.$toast("上传失败", "error"));
};
}
};
},
压缩图片
在IOS中，canvas绘制图片是有两个限制的：
首先是图片的大小，如果图片的大小超过两百万像素，图片也是无法绘制到canvas上的，调用drawImage的时候不会报错，但是你用toDataURL获取图片数据的时候获取到的是空的图片数据。
再者就是canvas的大小有限制，如果canvas的大小大于大概五百万像素（即宽高乘积）的时候，不仅图片画不出来，其他什么东西也都是画不出来的。
应对第一种限制，处理办法就是瓦片绘制了。瓦片绘制，也就是将图片分割成多块绘制到canvas上，我代码里的做法是把图片分割成100万像素一块的大小，再绘制到canvas上。
而应对第二种限制，我的处理办法是对图片的宽高进行适当压缩，我代码里为了保险起见，设的上限是四百万像素，如果图片大于四百万像素就压缩到小于四百万像素。四百万像素的图片应该够了，算起来宽高都有2000X2000了。
如此一来就解决了IOS上的两种限制了。
除了上面所述的限制，还有两个坑，一个就是canvas的toDataURL是只能压缩jpg的，当用户上传的图片是png的话，就需要转成jpg，也就是统一用canvas.toDataURL(‘image/jpeg', 0.1) ， 类型统一设成jpeg，而压缩比就自己控制了。
另一个就是如果是png转jpg，绘制到canvas上的时候，canvas存在透明区域的话，当转成jpg的时候透明区域会变成黑色，因为canvas的透明像素默认为rgba(0,0,0,0)，所以转成jpg就变成rgba(0,0,0,1)了，也就是透明背景会变成了黑色。解决办法就是绘制之前在canvas上铺一层白色的底色。
_compress(img) {
let canvas = document.createElement("canvas");
let ctx = canvas.getContext("2d");
//瓦片
let tCanvas = document.createElement("canvas");
let tctx = tCanvas.getContext("2d");
let initSize = img.src.length;
let width = img.width;
let height = img.height;
//如果图片大于四百万像素，计算压缩比并将大小压至400万以下
let ratio;
if ((ratio = (width * height) / 4000000) > 1) {
ratio = Math.sqrt(ratio);
widht /= ratio;
height /= ratio;
} else {
ratio = 1;
}
canvas.width = width;
canvas.height = height;
//铺底色
ctx.fillStyle = "#fff";
ctx.fillRect(0, 0, canvas.width, canvas.height);
//如果图片像素大于100万则使用瓦片绘制
let count;
if ((count = (width * height) / 1000000) > 1) {
count = ~~(Math.sqrt(count) + 1); //计算要分成多少瓦片，~~在这里表示取整
//计算每块瓦片的宽高
let nw = ~~(width / count);
let nh = ~~(height / count);
tCanvas.width = nw;
tCanvas.height = nh;
for (let i = 0; i < count; i++) {
for (let j = 0; j < count; j++) {
tctx.drawImage(
img, i * nw * ratio, j * nh * ratio, nw * ratio,nh * ratio, 0, 0, nw,nh
);
ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
}
}
} else {
ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
}
//进行压缩
let ndata = canvas.toDataURL("image/jpeg", 0.3);
tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
return ndata;
},
上传
完成图片压缩后，就可以塞进formdata里进行上传了，先将base64数据转成字符串，再实例化一个ArrayBuffer，然后将字符串以8位整型的格式传入ArrayBuffer，再通过BlobBuilder或者Blob对象，将8位整型的ArrayBuffer转成二进制对象blob，再将blob转为File对象
_upload(data, name, type) {
let text = window.atob(data.split(",")[1]);
let buffer = new ArrayBuffer(text.length);
let ubuffer = new Uint8Array(buffer);
let pecent = 0,
loop = null;
for (var i = 0; i < text.length; i++) {
ubuffer[i] = text.charCodeAt(i);
}
let Builder =
window.BlobBuilder ||
window.WebKitBlobBuilder ||
window.MozBlobBuilder ||
window.MSBlobBuilder;
let blob;
if (Builder) {
var builder = new Builder();
builder.append(buffer);
blob = builder.getBlob(type);
} else {
blob = new window.Blob([ubuffer], { type: type });
}
// blob 转file
var fileOfBlob = new File([blob], name, { type: type });
return fileOfBlob;
}
}
将图片压缩上传封装到一个js文件里
const UploadImg = {
imageHandle(files, maxSize, imgDom) {
let that = this;
let formdata = new FormData();
let reader = new FileReader();
reader.readAsDataURL(files[0]); //将图片转成base64格式
//reader.onload是异步，要用到Promise对象将值返回出去
return new Promise((resolved, rejected) => {
reader.onload = function () {
let result = this.result;
let img = new Image();
img.src = result;
if (this.result.length <= maxSize) {
imgDom.src = result;
img = null;
formdata.append("image", that._upload(result, files[0].name, files[0].type));
resolved(formdata);
} else {
img.onload = function () {
let data = that._compress(img);
imgDom.src = data;
formdata.append("image", that._upload(data, files[0].name, files[0].type));
resolved(formdata);
};
}
};
})
},
_compress(img) {
let canvas = document.createElement("canvas");
let ctx = canvas.getContext("2d");
//瓦片
let tCanvas = document.createElement("canvas");
let tctx = tCanvas.getContext("2d");
let width = img.width;
let height = img.height;
//如果图片大于四百万像素，计算压缩比并将大小压至400万以下
let ratio;
if ((ratio = (width * height) / 4000000) > 1) {
ratio = Math.sqrt(ratio);
widht /= ratio;
height /= ratio;
} else {
ratio = 1;
}
canvas.width = width;
canvas.height = height;
//铺底色
ctx.fillStyle = "#fff";
ctx.fillRect(0, 0, canvas.width, canvas.height);
//如果图片像素大于100万则使用瓦片绘制
let count;
if ((count = (width * height) / 1000000) > 1) {
count = ~~(Math.sqrt(count) + 1); //计算要分成多少瓦片
//计算每块瓦片的宽高
let nw = ~~(width / count);
let nh = ~~(height / count);
tCanvas.width = nw;
tCanvas.height = nh;
for (let i = 0; i < count; i++) {
for (let j = 0; j < count; j++) {
tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
}
}
} else {
ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
}
//进行最小压缩
let ndata = canvas.toDataURL("image/jpeg", 0.3);
tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
return ndata;
},
_upload(data, name, type) {
let text = window.atob(data.split(",")[1]);
let buffer = new ArrayBuffer(text.length);
let ubuffer = new Uint8Array(buffer);
for (var i = 0; i < text.length; i++) {
ubuffer[i] = text.charCodeAt(i);
}
let Builder =
window.BlobBuilder ||
window.WebKitBlobBuilder ||
window.MozBlobBuilder ||
window.MSBlobBuilder;
let blob;
if (Builder) {
var builder = new Builder();
builder.append(buffer);
blob = builder.getBlob(type);
} else {
blob = new window.Blob([ubuffer], { type: type });
}
// blob 转file
var fileOfBlob = new File([blob], name, { type: type });
return fileOfBlob;
}
}
export default UploadImg
调用代码
import UploadImg from "../../util/uploadImg";
methods: {
imageHandle(e) {
let maxSize = 100 * 1024;
let imgDom = this.$refs.upImg;
let files = e.srcElement.files;
if (!files.length) return; //文件长度大于0
if (!/^image\//.test(files[0].type)) return; //必须是图片才处理
if (!window.FileReader) return; //支持FileReader
if (this.docEntry === "" || this.lineId === "") {
this.$toast("请填写完整信息", "error");
return;
}
// let formdata = new FormData();
UploadImg.imageHandle(files, maxSize, imgDom).then(formdata => {
formdata.append("docEntry", this.docEntry);
formdata.append("lineId", this.lineId);
formdata.append("action", "ProductionListImage");
this.$store
.dispatch("uploadImage", formdata)
.then(data => {
if (data === 1) {
this.$toast("上传成功", "success");
} else if (data === -1) {
this.$toast("图片为空", "error");
} else {
this.$toast("上传失败", "error");
}
})
.catch(error => this.$toast("上传失败", "error"));
});
}
}
参考链接：移动端利用H5实现压缩图片上传功能
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