JavaScript method to write files to local

Sometimes you need to save files locally through JavaScript at work. We all know that JavaScript is not allowed to directly operate local files due to security considerations. IE can use a VB plug-in, but neither Chrome nor Firefox supports JavaScript to write files locally, so there are compatibility issues with the VB plug-in.

Is there a suitable method? The answer is yes, we can achieve our needs through the small plug-in FileSaver.js. Let’s look at a specific piece of code:

/**
 * 下载文件
 */
var downloadTextFile = function(mobileCode) {
  if(isEmpty(mobileCode)) {
    mobileCode = '';
  }
  var file = new File([mobileCode], "手机号.txt", { type: "text/plain;charset=utf-8" });
  saveAs(file);
}

This example is to store a text file named "Mobile phone number.txt" locally, using the character encoding format of " UTF-8", thus avoiding the problem of Chinese garbled characters. If you are smart, try it now!

Attached is the complete source code of the FileSaver.js file:

/* FileSaver.js
 * A saveAs() FileSaver implementation.
 * 1.3.2
 * 2016-06-16 18:25:19
 *
 * By Eli Grey, http://eligrey.com
 * License: MIT
 *  See https://github.com/eligrey/FileSaver.js/blob/master/LICENSE.md
 */
/*global self */
/*jslint bitwise: true, indent: 4, laxbreak: true, laxcomma: true, smarttabs: true, plusplus: true */
/*! @source http://purl.eligrey.com/github/FileSaver.js/blob/master/FileSaver.js */
var saveAs = saveAs || (function(view) {
  "use strict";
  // IE <10 is explicitly unsupported
  if (typeof view === "undefined" || typeof navigator !== "undefined" && /MSIE [1-9]\./.test(navigator.userAgent)) {
    return;
  }
  var
     doc = view.document
     // only get URL when necessary in case Blob.js hasn&#39;t overridden it yet
    , get_URL = function() {
      return view.URL || view.webkitURL || view;
    }
    , save_link = doc.createElementNS("http://www.w3.org/1999/xhtml", "a")
    , can_use_save_link = "download" in save_link
    , click = function(node) {
      var event = new MouseEvent("click");
      node.dispatchEvent(event);
    }
    , is_safari = /constructor/i.test(view.HTMLElement) || view.safari
    , is_chrome_ios =/CriOS\/[\d]+/.test(navigator.userAgent)
    , throw_outside = function(ex) {
      (view.setImmediate || view.setTimeout)(function() {
        throw ex;
      }, 0);
    }
    , force_saveable_type = "application/octet-stream"
    // the Blob API is fundamentally broken as there is no "downloadfinished" event to subscribe to
    , arbitrary_revoke_timeout = 1000 * 40 // in ms
    , revoke = function(file) {
      var revoker = function() {
        if (typeof file === "string") { // file is an object URL
          get_URL().revokeObjectURL(file);
        } else { // file is a File
          file.remove();
        }
      };
      setTimeout(revoker, arbitrary_revoke_timeout);
    }
    , dispatch = function(filesaver, event_types, event) {
      event_types = [].concat(event_types);
      var i = event_types.length;
      while (i--) {
        var listener = filesaver["on" + event_types[i]];
        if (typeof listener === "function") {
          try {
            listener.call(filesaver, event || filesaver);
          } catch (ex) {
            throw_outside(ex);
          }
        }
      }
    }
    , auto_bom = function(blob) {
      // prepend BOM for UTF-8 XML and text/* types (including HTML)
      // note: your browser will automatically convert UTF-16 U+FEFF to EF BB BF
      if (/^\s*(?:text\/\S*|application\/xml|\S*\/\S*\+xml)\s*;.*charset\s*=\s*utf-8/i.test(blob.type)) {
        return new Blob([String.fromCharCode(0xFEFF), blob], {type: blob.type});
      }
      return blob;
    }
    , FileSaver = function(blob, name, no_auto_bom) {
      if (!no_auto_bom) {
        blob = auto_bom(blob);
      }
      // First try a.download, then web filesystem, then object URLs
      var
         filesaver = this
        , type = blob.type
        , force = type === force_saveable_type
        , object_url
        , dispatch_all = function() {
          dispatch(filesaver, "writestart progress write writeend".split(" "));
        }
        // on any filesys errors revert to saving with object URLs
        , fs_error = function() {
          if ((is_chrome_ios || (force && is_safari)) && view.FileReader) {
            // Safari doesn&#39;t allow downloading of blob urls
            var reader = new FileReader();
            reader.onloadend = function() {
              var url = is_chrome_ios ? reader.result : reader.result.replace(/^data:[^;]*;/, &#39;data:attachment/file;&#39;);
              var popup = view.open(url, &#39;_blank&#39;);
              if(!popup) view.location.href = url;
              url=undefined; // release reference before dispatching
              filesaver.readyState = filesaver.DONE;
              dispatch_all();
            };
            reader.readAsDataURL(blob);
            filesaver.readyState = filesaver.INIT;
            return;
          }
          // don&#39;t create more object URLs than needed
          if (!object_url) {
            object_url = get_URL().createObjectURL(blob);
          }
          if (force) {
            view.location.href = object_url;
          } else {
            var opened = view.open(object_url, "_blank");
            if (!opened) {
              // Apple does not allow window.open, see https://developer.apple.com/library/safari/documentation/Tools/Conceptual/SafariExtensionGuide/WorkingwithWindowsandTabs/WorkingwithWindowsandTabs.html
              view.location.href = object_url;
            }
          }
          filesaver.readyState = filesaver.DONE;
          dispatch_all();
          revoke(object_url);
        }
      ;
      filesaver.readyState = filesaver.INIT;
      if (can_use_save_link) {
        object_url = get_URL().createObjectURL(blob);
        setTimeout(function() {
          save_link.href = object_url;
          save_link.download = name;
          click(save_link);
          dispatch_all();
          revoke(object_url);
          filesaver.readyState = filesaver.DONE;
        });
        return;
      }
      fs_error();
    }
    , FS_proto = FileSaver.prototype
    , saveAs = function(blob, name, no_auto_bom) {
      return new FileSaver(blob, name || blob.name || "download", no_auto_bom);
    }
  ;
  // IE 10+ (native saveAs)
  if (typeof navigator !== "undefined" && navigator.msSaveOrOpenBlob) {
    return function(blob, name, no_auto_bom) {
      name = name || blob.name || "download";
      if (!no_auto_bom) {
        blob = auto_bom(blob);
      }
      return navigator.msSaveOrOpenBlob(blob, name);
    };
  }
  FS_proto.abort = function(){};
  FS_proto.readyState = FS_proto.INIT = 0;
  FS_proto.WRITING = 1;
  FS_proto.DONE = 2;
  FS_proto.error =
  FS_proto.onwritestart =
  FS_proto.onprogress =
  FS_proto.onwrite =
  FS_proto.onabort =
  FS_proto.onerror =
  FS_proto.onwriteend =
    null;
  return saveAs;
}(
    typeof self !== "undefined" && self
  || typeof window !== "undefined" && window
  || this.content
));
// `self` is undefined in Firefox for Android content script context
// while `this` is nsIContentFrameMessageManager
// with an attribute `content` that corresponds to the window
if (typeof module !== "undefined" && module.exports) {
 module.exports.saveAs = saveAs;
} else if ((typeof define !== "undefined" && define !== null) && (define.amd !== null)) {
 define("FileSaver.js", function() {
  return saveAs;
 });
}

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