ionic3 使用html2canvas將數據導出為圖片，並下載本地

1、安裝html2canvas

npm install --save html2canvas
官方網站
https://html2canvas.hertzen.com/

2、在需要的組件中引入html2canvas

// 導入整個模塊的內容
import  html2canvas from 'html2canvas';
3、定義方法，將數據轉換為canvas

let  element:any = document.querySelector("#mainTable");
//要顯示圖片的img標簽
let image:any = document.querySelector('#img');
//調用html2image方法
html2canvas(element).then( canvas=> {

this.canvasImg = canvas.toDataURL("image/png");

}）
// 然后給初始化的public canvasImg: any = ""; 復制，他就是圖片地址。 // 展示圖片 <img src="{{canvasImg}}" />

4、將圖片下載到本地，定義轉換圖片格式方法。 
下載cordova插件
$ ionic cordova plugin add cordova-plugin-photo-library --variable PHOTO_LIBRARY_USAGE_DESCRIPTION="To choose photos"
$ npm install --save @ionic-native/photo-library
導入
import { PhotoLibrary } from '@ionic-native/photo-library';
this.photoLibrary.requestAuthorization().then(() => {
    this.photoLibrary.saveImage(this.canvasImg , 'NewPayQr', '').then((libraryItem)=>{
        this.commonUtils.alertCommon('', this.translateObj.saveImgSucc);
        // alert(JSON.stringify(libraryItem));
        console.log(libraryItem.id);          // ID of the photo
        console.log(libraryItem.photoURL);    // Cross-platform access to photo
        console.log(libraryItem.thumbnailURL);// Cross-platform access to thumbnail
        console.log(libraryItem.fileName);
        console.log(libraryItem.width);
        console.log(libraryItem.height);
        console.log(libraryItem.creationDate);
        console.log(libraryItem.latitude);
        console.log(libraryItem.longitude);
        console.log(libraryItem.albumIds);    // array of ids of appropriate AlbumItem, only of includeAlbumsData was used
    });
}).catch(err =>{
    console.log('permissions weren\'t granted')
    this.commonUtils.alertCommon('',this.translateObj.saveImgFail+','+err);
} );