1.语法：function 用var, let, const来表示参数要希望在第一个等号的后面
2.如果没有参数，需要写一对空的括号
3.只有一个参数，那就直接写，不用加括号
4.参数有多个，需要加一个小括号，参数用逗号隔开
5.函数的主体内容是放在箭头后面，如果语句只有一条，那就直接写，如果语句有多条，需要把他们放在一对大括号里
参考资料： https://www.51zxw.com/
纯js不好实现,但是配合html,css就有了近似的办法.下面提供一个解决方案,已知两个点的坐标,为它们画一条带箭头的弧线.
<html>
<head>
<meta http-equiv = "content-type" content = "text/htmlcharset = gb2312">
<title>箭头弧线</title>
<style type = "text/css">
span { position: absolutewidth: 5pxheight: 5pxbackground-color: #0000ffdisplay: blockborder-radius: 50%}
</style>
<script language = "javascript">
function locateO () {
var x0 = parseInt (spnA.style.left, 10), y0 = parseInt (spnA.style.top, 10), x1 = parseInt (spnB.style.left, 10), y1 = parseInt (spnB.style.top, 10), horizontalDistance = Math.abs (x1 - x0), verticalDistance = Math.abs (y1 - y0), x = Math.min (x0, x1) + horizontalDistance / 2, y = Math.min (y0, y1) + verticalDistance / 2, distance = Math.sqrt (Math.pow (horizontalDistance, 2) + Math.pow (verticalDistance, 2)), array = new Array (x0, y0, x1, y1, distance)
spnO.style.left = x
spnO.style.top = y
return array
}
function getRadian (x0, y0, x1, y1) {
var horizontalDistance = Math.abs (x1 - x0), verticalDistance = Math.abs (y1 - y0), rate = horizontalDistance == 0 ? 0 : verticalDistance / horizontalDistance, radian
if (y1 <y0) {
if (x1 >x0) {
radian = - Math.atan (rate)
} else if (x1 == x0) {
radian = - Math.PI / 2
} else {
radian = - (Math.PI - Math.atan (rate))
}
} else if (y1 == y0) {
radian = x1 >left ? 0 : - Math.PI
} else if (x1 <x0) {
radian = - (Math.PI + Math.atan (rate))
} else if (x1 == x0) {
radian = - Math.PI * 3 / 2
} else {
radian = - 2 * Math.PI + Math.atan (rate)
}
return radian
}
function getAngle (radian) {
var angle = - radian * 180 / Math.PI
return angle
}
function slantArc (x0, y0, x1, y1) {
var radian = getRadian (x0, y0, x1, y1), angle = 360 - getAngle (radian)
cnvArc.style.transform = "rotate(" + angle + "deg)"
}
function drawArc (x0, y0, width) {
var context = cnvArc.getContext ("2d"), radius = width / 2, height = radius / 2
cnvArc.width = width + 10
cnvArc.height = height
cnvArc.style.left = x0
cnvArc.style.top = y0 - height
context.ellipse (radius + 5, height, radius, height / 2, 0, 0, Math.PI * 2)
context.strokeStyle = "#00ff00"
context.stroke ()
}
function hex (figure) {
return figure.toString (16)
}
function zeroize (cluster) {
if (cluster.length <2) {
cluster = 0 + cluster
}
return cluster
}
function getColour (red, green, blue) {
return "#" + zeroize (hex (red)) + zeroize (hex (green)) + zeroize (hex (blue))
}
function printArc () {
var width = cnvArc.width, height = cnvArc.height, context = cnvArc.getContext ("2d"), imageData = context.getImageData (0, 0, width, height), data = imageData.data, coordinates = new Array (), cluster = "", i, red, green, blue, colour, index, x, y
for (i = 0i <data.lengthi += 4) {
red = data [i]
green = data [i + 1]
blue = data [i + 2]
colour = getColour (red, green, blue)
index = i / 4
y = parseInt (index / width, 10)
x = index % width
if (x == 0) {
//console.log (y + "\n" + cluster)
cluster = ""
}
cluster += x + ":" + colour + " "
if (colour == "#00ff00") {
coordinates.push (new Array (x, y))
}
}
return coordinates
}
function sortCoordinates (coordinates, direction) {
var i = 0, flag, j, coordinate
do {
flag = false
for (j = 0j <coordinates.length - 1 - ij ++) {
if (direction &&(coordinates [j] [0] >coordinates [j + 1] [0] || coordinates [j] [0] == coordinates [j + 1] [0] &&coordinates [j] [1] >coordinates [j + 1] [1]) || ! direction &&(coordinates [j] [0] <coordinates [j + 1] [0] || coordinates [j] [0] == coordinates [j + 1] [0] &&coordinates [j] [1] >coordinates [j + 1] [1])) {
coordinate = coordinates [j]
coordinates [j] = coordinates [j + 1]
coordinates [j + 1] = coordinate
flag = true
}
}
i ++
} while (flag)
}
function drawArrow (x0, y0, x1, y1) {
var context = cnvArc.getContext ("2d"), colour = "#00ff00", angle = (x1 - x0) / (y1 - y0)
context.strokeStyle = colour
context.fillStyle = colour
context.setLineDash ([3, 3])
context.beginPath ()
context.arc (x0, y0, 1, 0, 2 * Math.PI)
context.translate (0, 0, 0)
context.moveTo (x0, y0)
context.lineTo (x1, y1)
context.fill ()
context.stroke ()
context.save ()
context.translate (x1, y1)
angle = Math.atan (angle)
context.rotate ((y1 >= y0 ? 0 : Math.PI) - angle)
context.lineTo (- 3, - 9)
context.lineTo (0, - 3)
context.lineTo (3, - 9)
context.lineTo (0, 0)
context.fill ()
context.restore ()
context.closePath ()
}
function initialize () {
var array = locateO (), x0 = array [0], y0 = array [1], x1 = array [2], y1 = array [3], width = array [4], direction = x1 >x0, coordinates, length, coordinate0, coordinate1, x2, y2, x3, y3
drawArc (x0, y0, width)
coordinates = printArc ()
length = coordinates.length
sortCoordinates (coordinates, direction)
coordinate0 = coordinates [length - 2]
x2 = coordinate0 [0]
y2 = coordinate0 [1]
coordinate1 = coordinates [length - 1]
x3 = coordinate1 [0]
y3 = coordinate1 [1]
drawArrow (x2, y2, x3, y3)
slantArc (x0, y0, x1, y1)
}
</script>
</head>
<body style = "margin: 0" onload = "initialize ()">
<span id = "spnA" style = "left: 50pxtop: 150px"></span>
<span id = "spnB" style = "left: 850pxtop: 350px"></span>
<span id = "spnO"></span>
<canvas id = "cnvArc" style = "position: absolutebackground-color: rgb(255, 255, 0, 0.01)z-index: 1transform-origin: 0 100%"></canvas>
</body>
</html>
复制进来的代码都不带缩进的吗?
该代码纯手写,不从第三方处盗用.仅供参考.
