解決微信及360瀏覽器沒法讀取本地圖片問題

時間 2019-11-09

原文原文鏈接

近期作移動端項目發現360瀏覽器及微信不能讀取本地圖片，究其緣由是沒法獲取文件格式，致使base64編碼時文件頭丟失文件類型信息，沒法生成正確的圖片編碼，因此添加文件頭便可解決此問題。html

正確的編碼canvas

data:image/jpeg;base64,...瀏覽器

微信的編碼微信

data:;base64,...函數

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=0">
<title>圖片壓縮</title>
<style>
body { margin:0; padding:0; }
html { font-size:62.5%; }

.imgzip { padding:1em; }
.imgzip .itm { padding-bottom:1em; word-break:break-all; font-size:1.2rem; line-height:1.5em; }
.imgzip .itm .tit { margin-bottom:.5em; background-color:#e71446; color:#FFF; padding:.5rem 1rem; border-radius:3px; }
.imgzip .itm .cnt { padding:1rem; }
.imgzip .itm .cnt img { display:block; max-width:100%; }
.imgzip textarea { width:100%; height:20em; }
</style>
</head>

<body>
<input type="file" accept="image/*;capture=camera" class="input">
<div class="imgzip"></div>
<script>
document.addEventListener('DOMContentLoaded', init, false);

function init() {
  var u = new UploadPic();
  u.init({
    input: document.querySelector('.input'),
    callback: function (base64) {
      var html = '';
            
      html = '<div class="itm"><div class="tit">圖片名稱：</div><div class="cnt">' + this.fileName + '</div></div>'
           + '<div class="itm"><div class="tit">原始大小：</div><div class="cnt">' + (this.fileSize / 1024).toFixed(2) + 'KB<\/div><\/div>'
           + '<div class="itm"><div class="tit">編碼大小：</div><div class="cnt">' + (base64.length / 1024).toFixed(2) + 'KB<\/div><\/div>'
           + '<div class="itm"><div class="tit">原始尺寸：</div><div class="cnt">' + this.tw + 'px * ' + this.th + 'px<\/div><\/div>'
           + '<div class="itm"><div class="tit">編碼尺寸：</div><div class="cnt">' + this.sw + 'px * ' + this.sh + 'px<\/div><\/div>'
           + '<div class="itm"><div class="tit">圖片預覽：</div><div class="cnt"><img src="' + base64 + '"><\/div><\/div>'
           + '<div class="itm"><div class="tit">Base64編碼：</div><div class="cnt"><textarea>' + base64 + '<\/textarea><\/div><\/div>';

      document.querySelector('.imgzip').innerHTML = html;
    },
    loading: function () {
      document.querySelector('.imgzip').innerHTML = '讀取中，請稍候...';
    }
  });
}

function UploadPic() {
  this.sw = 0;
  this.sh = 0;
  this.tw = 0;
  this.th = 0;
  this.scale = 0;
  this.maxWidth = 0;
  this.maxHeight = 0;
  this.maxSize = 0;
  this.fileSize = 0;
  this.fileDate = null;
  this.fileType = '';
  this.fileName = '';
  this.input = null;
  this.canvas = null;
  this.mime = {};
  this.type = '';
  this.callback = function () {};
  this.loading = function () {};
}

UploadPic.prototype.init = function (options) {
  this.maxWidth = options.maxWidth || 800;
  this.maxHeight = options.maxHeight || 600;
  this.maxSize = options.maxSize || 3 * 1024 * 1024;
  this.input = options.input;
  this.mime = {'png': 'image/png', 'jpg': 'image/jpeg', 'jpeg': 'image/jpeg', 'bmp': 'image/bmp'};
  this.callback = options.callback || function () {};
  this.loading = options.loading || function () {};
    
  this._addEvent();
};

/**
 * @description 綁定事件
 * @param {Object} elm 元素
 * @param {Function} fn 綁定函數
 */
UploadPic.prototype._addEvent = function () {
  var _this = this;
    
  function tmpSelectFile(ev) {
    _this._handelSelectFile(ev);
  }
    
  this.input.addEventListener('change', tmpSelectFile, false);
};

/**
 * @description 綁定事件
 * @param {Object} elm 元素
 * @param {Function} fn 綁定函數
 */
UploadPic.prototype._handelSelectFile = function (ev) {
  var file = ev.target.files[0];
  
  this.type = file.type
  
  // 若是沒有文件類型，則經過後綴名判斷（解決微信及360瀏覽器沒法獲取圖片類型問題）
  if (!this.type) {
    this.type = this.mime[file.name.match(/\.([^\.]+)$/i)[1]];
  }
  
  if (!/image.(png|jpg|jpeg|bmp)/.test(this.type)) {
    alert('選擇的文件類型不是圖片');
    return;
  }
    
  if (file.size > this.maxSize) {
    alert('選擇文件大於' + this.maxSize / 1024 / 1024 + 'M，請從新選擇');
    return;
  }

  this.fileName = file.name;
  this.fileSize = file.size;
  this.fileType = this.type;
  this.fileDate = file.lastModifiedDate;
    
  this._readImage(file);
};

/**
 * @description 讀取圖片文件
 * @param {Object} image 圖片文件
 */
UploadPic.prototype._readImage = function (file) {
  var _this = this;
    
  function tmpCreateImage(uri) {
    _this._createImage(uri);
  }
  
  this.loading();
    
  this._getURI(file, tmpCreateImage);
};

/**
 * @description 經過文件得到URI
 * @param {Object} file 文件
 * @param {Function} callback 回調函數，返回文件對應URI
 * return {Bool} 返回false
 */
UploadPic.prototype._getURI = function (file, callback) {
  var reader = new FileReader();
  var _this = this;

  function tmpLoad() {
    // 頭不帶圖片格式，需填寫格式
    var re = /^data:base64,/;
    var ret = this.result + '';
        
    if (re.test(ret)) ret = ret.replace(re, 'data:' + _this.mime[_this.fileType] + ';base64,');
        
    callback && callback(ret);
  }
    
  reader.onload = tmpLoad;
    
  reader.readAsDataURL(file);
    
  return false;
};

/**
 * @description 建立圖片
 * @param {Object} image 圖片文件
 */
UploadPic.prototype._createImage = function (uri) {
  var img = new Image();
  var _this = this;
    
  function tmpLoad() {
    _this._drawImage(this);
  }
    
  img.onload = tmpLoad;
    
  img.src = uri;
};

/**
 * @description 建立Canvas將圖片畫至其中，並得到壓縮後的文件
 * @param {Object} img 圖片文件
 * @param {Number} width 圖片最大寬度
 * @param {Number} height 圖片最大高度
 * @param {Function} callback 回調函數，參數爲圖片base64編碼
 * return {Object} 返回壓縮後的圖片
 */
UploadPic.prototype._drawImage = function (img, callback) {
  this.sw = img.width;
  this.sh = img.height;
  this.tw = img.width;
  this.th = img.height;
    
  this.scale = (this.tw / this.th).toFixed(2);

  if (this.sw > this.maxWidth) {
    this.sw = this.maxWidth;
    this.sh = Math.round(this.sw / this.scale);
  }
  
  if (this.sh > this.maxHeight) {
    this.sh = this.maxHeight;
    this.sw = Math.round(this.sh * this.scale);
  }
  
  this.canvas = document.createElement('canvas');
  var ctx = this.canvas.getContext('2d');
    
  this.canvas.width = this.sw;
  this.canvas.height = this.sh;
    
  ctx.drawImage(img, 0, 0, img.width, img.height, 0, 0, this.sw, this.sh);
    
  this.callback(this.canvas.toDataURL(this.type));
    
  ctx.clearRect(0, 0, this.tw, this.th);
  this.canvas.width = 0;
  this.canvas.height = 0;
  this.canvas = null;
};
</script>
</body>
</html>