【解决】canvasToTempFilePath:fail fail canvas is empty

uni.canvasToTempFilePath({}, this);加个this

uni.canvasToTempFilePath({  
    canvasId: "canvas",  
    success: (res) => {  
        console.log('canvas转成图片成功：', res);  
    },  
    fail: (err) => {  
        console.log('canvas转成图片失败：', err)  
    }  
}, this)

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