beZierCurveTo(num1, num2, num3, num4, x, y)
quadraticCurveTo(num1, num2, x, y)

A1[M[i-1][0] + a*(M[i][0] - M[i-2][0]), M[i-1][1] + b*(M[i][1] - M[i-2][1])]

A2[M[i][0] - b*(M[i+1][0] - M[i-1][0]), M[i][1] - b*(M[i+1][1] - M[i-1][1])]

bezierLine (canvasId, options) {
let windowWidth = 0
wx.getSystemInfo({
 success (result) {
  windowWidth = result.windowWidth
 }
})
let a = windowWidth / (options.xAxis.length-1)
let data = []
options.xAxis.map((item, i) => {
 data.push([i * a, 200 - options.yAxis[i]])
})
data.unshift(data[0])
data.push(data[data.length - 1])

const ctx = wx.createCanvasContext(canvasId)
ctx.beginPath()
data.map((item, i) => {
 const a = 0.25
 const b = 0.25
 if (i == 0 || i == data.length - 1) {
  // do nothing
 } else if (i == 1) {
  ctx.moveTo(item[0], item[1])
 } else {
  const a1 = data[i - 1][0] + a * (data[i][0] - data[i - 2][0])
  const a2 = data[i - 1][1] + b * (data[i][1] - data[i - 2][1])
  const b1 = data[i][0] - b * (data[i + 1][0] - data[i - 1][0])
  const b2 = data[i][1] - b * (data[i + 1][1] - data[i - 1][1])
  ctx.bezierCurveTo(a1, a2, b1, b2, item[0], item[1])
 }
})
ctx.setLineWidth(1)
ctx.setStrokeStyle('red')
ctx.stroke()
ctx.draw()
}
// 在onLoad中调用
this.bezierLine('stage', {
 xAxis: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30],
 yAxis: [11, 33, 22, 32, 14, 15, 20, 60, 23, 44, 77, 122, 133, 89, 156, 122,128, 143, 111, 101, 132, 99, 98, 44, 62, 74, 111, 13, 42, 55]
})