FileSaver.js可以实现前端导出文件的需求。

使用方法：

1.保存文件

//obj是我们想写入文件的内容。
let blob = new Blob([JSON.stringify(obj)], {type: "text/plain;charset=utf-8"});
saveAs(blob, "文件导出测试.txt");

2.保存图片

//将canvas内容保存为文件并下载
canvas.toBlob(function(blob) { saveAs(blob, "hangge.png");});

reacrt引入方式

import {saveAs} from "./FileSaver";

FileSaver.js可以作为一个js文件引入，也可用用npm安装。

npm install file-saver --save
bower install file-saver

浏览器支持情况

Browser	Constructs as	Filenames	Max Blob Size	Dependencies
Firefox 20+	Blob	Yes	800 MiB	None
Firefox < 20	data: URI	No	n/a	Blob.js
Chrome	Blob	Yes	500 MiB	None
Chrome for Android	Blob	Yes	500 MiB	None
Edge	Blob	Yes	?	None
IE 10+	Blob	Yes	600 MiB	None
Opera 15+	Blob	Yes	500 MiB	None
Opera < 15	data: URI	No	n/a	Blob.js
Safari 6.1+*	Blob	No	?	None
Safari < 6	data: URI	No	n/a	Blob.js
Safari 10.1+	Blob	Yes	n/a	None

源码：

/* FileSaver.js
 * A saveAs() FileSaver implementation.
 * 1.3.8
 * 2018-03-22 14:03:47
 *
 * By Eli Grey, https://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/src/FileSaver.js */

export 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'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)
        , setImmediate = view.setImmediate || view.setTimeout
        , throw_outside = function(ex) {
            setImmediate(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't allow downloading of blob urls
                        var reader = new FileReader();
                        reader.onloadend = function() {
                            var url = is_chrome_ios ? reader.result : reader.result.replace(/^data:[^;]*;/, 'data:attachment/file;');
                            var popup = view.open(url, '_blank');
                            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'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);
                setImmediate(function() {
                    save_link.href = object_url;
                    save_link.download = name;
                    click(save_link);
                    dispatch_all();
                    revoke(object_url);
                    filesaver.readyState = filesaver.DONE;
                }, 0);
                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);
        };
    }

    // todo: detect chrome extensions & packaged apps
    //save_link.target = "_blank";

    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
));