overseas/plugin/image-tools/index.js

function getLocalFilePath(path) {
	if (path.indexOf('_www') === 0 || path.indexOf('_doc') === 0 || path.indexOf('_documents') === 0 || path.indexOf('_downloads') === 0) {
		return path
	}
	if (path.indexOf('file://') === 0) {
		return path
	}
	if (path.indexOf('/storage/emulated/0/') === 0) {
		return path
	}
	if (path.indexOf('/') === 0) {
		var localFilePath = plus.io.convertAbsoluteFileSystem(path)
		if (localFilePath !== path) {
				return localFilePath
		} else {
				path = path.substr(1)
		}
	}
	return '_www/' + path
}

export function pathToBase64(path) {
  return new Promise(function(resolve, reject) {
		if (typeof window === 'object' && 'document' in window) {
			if (typeof FileReader === 'function') {
				var xhr = new XMLHttpRequest()
				xhr.open('GET', path, true)
				xhr.responseType = 'blob'
				xhr.onload = function() {
					if (this.status === 200) {
						let fileReader = new FileReader()
						fileReader.onload = function(e) {
							resolve(e.target.result)
						}
						fileReader.onerror = reject
						fileReader.readAsDataURL(this.response)
					}
				}
				xhr.onerror = reject
				xhr.send()
				return
			}
			var canvas = document.createElement('canvas')
			var c2x = canvas.getContext('2d')
			var img = new Image
			img.onload = function() {
				canvas.width = img.width
				canvas.height = img.height
				c2x.drawImage(img, 0, 0)
				resolve(canvas.toDataURL())
				canvas.height = canvas.width = 0
			}
			img.onerror = reject
			img.src = path
			return
		}
		if (typeof plus === 'object') {
			plus.io.resolveLocalFileSystemURL(getLocalFilePath(path), function(entry) {
				entry.file(function(file) {
					var fileReader = new plus.io.FileReader()
					fileReader.onload = function(data) {
							resolve(data.target.result)
					}
					fileReader.onerror = function(error) {
							reject(error)
					}
					fileReader.readAsDataURL(file)
				}, function(error) {
					reject(error)
				})
			}, function(error) {
				reject(error)
			})
			return
		}
		if (typeof wx === 'object' && wx.canIUse('getFileSystemManager')) {
			wx.getFileSystemManager().readFile({
				filePath: path,
				encoding: 'base64',
				success: function(res) {
					resolve('data:image/png;base64,' + res.data)
				},
				fail: function(error) {
					reject(error)
				}
			})
			return
		}
		reject(new Error('not support'))
  })
}

export function base64ToPath(base64) {
	return new Promise(function(resolve, reject) {
		if (typeof window === 'object' && 'document' in window) {
			base64 = base64.split(',')
			var type = base64[0].match(/:(.*?);/)[1]
			var str = atob(base64[1])
			var n = str.length
			var array = new Uint8Array(n)
			while (n--) {
				array[n] = str.charCodeAt(n)
			}
			return resolve((window.URL || window.webkitURL).createObjectURL(new Blob([array], { type: type })))
		}
		var extName = base64.match(/data\:\S+\/(\S+);/)
		if (extName) {
			extName = extName[1]
		} else {
			reject(new Error('base64 error'))
		}
		var fileName = Date.now() + '.' + extName
		if (typeof plus === 'object') {
			var bitmap = new plus.nativeObj.Bitmap('bitmap' + Date.now())
			bitmap.loadBase64Data(base64, function() {
				var filePath = '_doc/uniapp_temp/' + fileName
				bitmap.save(filePath, {}, function() {
					bitmap.clear()
					resolve(filePath)
				}, function(error) {
					bitmap.clear()
					reject(error)
				})
			}, function(error) {
				bitmap.clear()
				reject(error)
			})
			return
		}
		if (typeof wx === 'object' && wx.canIUse('getFileSystemManager')) {
			var filePath = wx.env.USER_DATA_PATH + '/' + fileName
			wx.getFileSystemManager().writeFile({
				filePath: filePath,
				data: base64.replace(/^data:\S+\/\S+;base64,/, ''),
				encoding: 'base64',
				success: function() {
					resolve(filePath)
				},
				fail: function(error) {
					reject(error)
				}
			})
			return
		}
		reject(new Error('not support'))
  })
}