JavaScript對象/屬性

Question

我對JavaScript相當陌生，並且一直在使用HTML5元素。

問題是我現在正在使用一個庫來幫助簡化在多種設備（包括移動設備）上使用畫布，但是現在我有一個問題，因爲它看起來很簡單，米無法找到解決方案。我相信這可能是一個新手的錯誤，但這裏的交易：

我有這2個功能：

function drawLine(sX, sY, eX, eY) { 
    ctx.beginPath() 
    ctx.moveTo(sX, sY); 
    ctx.lineTo(eX, eY); 
    ctx.stroke(); 
    ctx.closePath(); 
    return { x: eX, y: eY }; 
} 

function canvas() { 
    var canvas = new Canvas ('canvas', 0, function() { 
     this.clear(); 
     this.setAutoResize(true); 
    }); 

    canvas.canvasElement.width = window.innerWidth; 
    canvas.canvasElement.height = window.innerHeight; 

    canvas.onTouchStart = function(start) { 
     var sX; var sY; 
     return {sX: start.clientX, sY: start.clientY}; 
    } 

    canvas.onTouchEnd = function (end) { 
     var eX; var eY; 
     return {eX: end.clientX, eY: end.clientY}; 
    } 

    // canvas.onTouchMove = drawLine(sX, sY, eX, eY); 
} 

沒有得到太多的細節，我怎麼能夠使用返回的值onTouchStart（）和onTouchEnd（）將x，y位置傳遞給drawLine函數？

所有我得到的是沒有定義的值，我真的在這裏失去了..

UPDATE：

@Juan門德斯，

感謝您的幫助，但沒看起來也不行。

爲了更好地理解的「背面」的代碼，這裏的touchstart事的例子：

this.canvasElement.addEventListener('touchstart', function(event) { 
    var touchCount = event.changedTouches.length; 
    var touches = []; 
    var touch = null; 

    for (var i = 0; i < touchCount; i++) { 
     touch = event.changedTouches[i]; 

     var touchInfo = { 
      pageX : touch.pageX, 
      pageY : touch.pageY, 
      clientX : touch.clientX, 
      clientY : touch.clientY, 
      screenX : touch.screenX, 
      screenY : touch.screenY, 
      target : touch.target, 
      identifier : touch.identifier 
     }; 

    self.onTouchStart(touchInfo, i, touchCount, event); 

    touches.push(touchInfo); 

    self.previousTouchInfo[touch.identifier] = touchInfo; 
    } 

    if (touchCount == 1) { 
     touch = event.changedTouches[0]; 

     var x = touch.clientX; 
     var y = touch.clientY; 

     if (self.touchEmulatesMouse) { 
      self.mouse.x = x; 
      self.mouse.y = y; 
      self.mouse.left = true; 

      if (self.layerParent != null) { 
       self.layerParent.onMouseDown(x, y, 0); 
      } 

     self.onMouseDown(x, y, 0); 
     } 
     } else { 
      self.onMultiTouchStart(touches, event); 
     } 
    }, false); 

/* A bit more down the library code */ 
/** 
* Called at the start of every touch start (including when multiple touches occured) 
* 
* The info object contains the folloring info: 
* - pageX - X coordinate relative to the full page (includes scrolling) 
* - pageY - Y coordinate relative to the full page (includes scrolling) 
* - clientX - X coordinate of touch relative to the viewport (excludes scroll offset) 
* - clientY - Y coordinate of touch relative to the viewport (excludes scroll offset) 
* - screenX - X coordinate relative to the screen 
* - screenY - Y coordinate relative to the screen 
* 
* @param {object} info Touch info 
* @param {integer} index Touch index 
* @param {integer} count The total number of active touches 
* @param {object} event The actual touch event 
*/ 
onTouchStart: function(info, index, count, event) {}, 

而且我也改變了我的代碼，以反映你的幫助，一些變化也使用嘗試touchInfo PARAM這樣的：

function createCanvas() { 
var canvas = new Canvas ('canvas', 0, function() { 
    this.clear(); 
    this.setAutoResize(true); 
}); 

var cWidth = canvas.canvasElement.width = window.innerWidth; 
var cHeight = canvas.canvasElement.height = window.innerHeight; 

var startPoint = null; 

function fill() { 
    canvas.fillStyle = "black"; 
    canvas.fillRect(0, 0, cWidth, cHeight); 
    canvas.beginPath(); 
} 

// Draw a line on the canvas from (s)tart to (e)nd 
function drawLine(sX, sY, eX, eY) { 
    canvas.beginPath() 
    canvas.moveTo(sX, sY); 
    canvas.lineTo(eX, eY); 
    canvas.stroke(); 
    canvas.closePath(); 
    //return { x: eX, y: eY }; 
} 

fill(); 

canvas.onTouchStart = function(start) { 
    startPoint = {sX: this.clientX, sY: this.clientY}; 
} 

canvas.onTouchEnd = function (end) { 
    drawLine(startPoint.sX, startPoint.sY, this.clientX, this.clientY); 
    // return {eX: end.clientX, eY: end.clientY}; 
} 
} 

任何幫助將是非常讚賞。在此先感謝

Answer 1

我終於設法解決了這個問題。原來這個庫沒有正確結束（還），我也沒有得到任何參數濫用這些函數。

Answer 2

很難告訴你要問什麼，但希望這有助於

我想你需要的是像下面

(function() { 
// Save the startPoint so we can use it when the touch ends to draw the line 
var startPoint; 
canvas.onTouchStart = function(e) { 
    // set the shared variable 
    startPoint = {x: e.clientX, y: e.clientY}; 
} 

canvas.onTouchEnd = function (e) { 
    drawLine(startPoint.x, startPoint.y, e.clientX, e.clientY); 
} 
})(); 

我認爲事件的名稱爲ontouchstart，不onTouchStart

這裏就是我想你的代碼應該看起來像

function drawLine(sX, sY, eX, eY) { 
    // Bad use of ctx global, you should pass it into the function so you can support 
    // multiple contexts 
    ctx.beginPath() 
    ctx.moveTo(sX, sY); 
    ctx.lineTo(eX, eY); 
    ctx.stroke(); 
    ctx.closePath(); 
    // Kind of silly to return this object, the caller already passed it in 
    // Should be used only if you need some kind of chaining, but 
    // makes for a weird API 
    return { x: eX, y: eY }; 
} 

// Don't name a function and a variable the same thing, 
// you had canvas as a variable and as a function. 
// They didn't cause a problem, but it's just not pretty to look at 
function createCanvas() {  
    var canvas = new Canvas('canvas', 0, function() { 
     this.clear(); 
     this.setAutoResize(true); 
    }); 

    canvas.canvasElement.width = window.innerWidth; 
    canvas.canvasElement.height = window.innerHeight; 


    // Save the startPoint so we can use it when the touch ends to draw the line 
    var startPoint; 
    // Correct spelling for ontouchstart 
    canvas.ontouchstart = function(start) { 
     // set the shared variable that will be used when they finish touching 
     startPoint = {x: e.clientX, y: e.clientY}; 
    } 

    // Draw the line 
    canvas.ontouchend = function (e) { 
     drawLine(startPoint.x, startPoint.y, e.clientX, e.clientY); 
    }  
} 

}