未定义onclick事件的函数-HTML5 canvas
[英]Function undefined for onclick event -HTML5 canvas
问题描述
I'm just starting out working with the HTML5 canvas and I want to use onclick to call as js function in my document. 
我刚开始使用HTML5画布，我想在文档中使用onclick作为js函数进行调用。
However, despite declaring the function in my JS, I still get [function name] is not defined when clicking. 但是，尽管在我的JS中声明了该函数，但单击时[function name] is not defined 。
The function is defined as such: 该函数的定义如下：
function draw_b() {
var b_canvas = document.getElementById("b"); // finds the canvas in the DOM
var b_context = b_canvas.getContext("2d"); // context for drawing. No 3D option yet
b_context.fillRect(50, 25, 150, 100);
}
The click event is included as such: 单击事件包括如下：
onclick="draw_b();return false"
Yet when I click the element, I get: 但是，当我单击该元素时，我得到：
draw_b is not defined
JSFiddle 的jsfiddle
3 个解决方案
解决方案1
3 已采纳 2015-10-14 17:56:35
In JSfiddle you need to use the No Wrap - In <head> option so the function is defined when used inline for the HTML elements. 在JSfiddle中，您需要使用No Wrap - In <head>选项，以便在将内联用于HTML元素时定义该函数。 Also var b_canvas = document.getElementById("b"); 另外var b_canvas = document.getElementById("b"); should be var b_canvas = document.getElementById("a"); 应该是var b_canvas = document.getElementById("a");
解决方案2
0 2015-10-14 17:56:12
您使用了错误的ID
var b_canvas = document.getElementById("a");// Use `a` not `b`
解决方案3
-1 2015-10-14 18:00:23
Jsfiddle doesn't like onclick="" so you need to use addEventListener from JavaScript. Jsfiddle不喜欢onclick=""因此您需要使用JavaScript中的addEventListener 。
var a_canvas = document.getElementById("a"); a_canvas.addEventListener("click",draw_b); function draw_b() { var b_canvas = document.getElementById("b"); // finds the canvas in the DOM var b_context = b_canvas.getContext("2d"); // context for drawing. No 3D option yet b_context.fillRect(50, 25, 150, 100); }
canvas { border: 1px dotted; }
<canvas id="a" width="300" height="225"></canvas> <canvas id="b" width="300" height="225"></canvas>
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