在JavaScript函数中定义全局变量

是否可以在JavaScript函数中定义全局变量?

我想在其他函数中使用trailimage变量(在makeObj函数中声明)。

<html xmlns="http://www.w3.org/1999/xhtml">
    <head id="Head1" runat="server">
        <title></title>
        <script type="text/javascript">
            var offsetfrommouse = [10, -20];
            var displayduration = 0;
            var obj_selected = 0;
            function makeObj(address) {
                **var trailimage = [address, 50, 50];**
                document.write('<img id="trailimageid" src="' + trailimage[0] + '" border="0"  style=" position: absolute; visibility:visible; left: 0px; top: 0px; width: ' + trailimage[1] + 'px; height: ' + trailimage[2] + 'px">');
                obj_selected = 1;
            }

            function truebody() {
                return (!window.opera && document.compatMode && document.compatMode != "BackCompat") ? document.documentElement : document.body;
            }
            function hidetrail() {
                var x = document.getElementById("trailimageid").style;
                x.visibility = "hidden";
                document.onmousemove = "";
            }
            function followmouse(e) {
                var xcoord = offsetfrommouse[0];
                var ycoord = offsetfrommouse[1];
                var x = document.getElementById("trailimageid").style;
                if (typeof e != "undefined") {
                    xcoord += e.pageX;
                    ycoord += e.pageY;
                }
                else if (typeof window.event != "undefined") {
                    xcoord += truebody().scrollLeft + event.clientX;
                    ycoord += truebody().scrollTop + event.clientY;
                }
                var docwidth = 1395;
                var docheight = 676;
                if (xcoord + trailimage[1] + 3 > docwidth || ycoord + trailimage[2] > docheight) {
                    x.display = "none";
                    alert("inja");
                }
                else
                    x.display = "";
                x.left = xcoord + "px";
                x.top = ycoord + "px";
            }

            if (obj_selected = 1) {
                alert("obj_selected = true");
                document.onmousemove = followmouse;
                if (displayduration > 0)
                    setTimeout("hidetrail()", displayduration * 1000);
            }
        </script>
    </head>
    <body>
        <form id="form1" runat="server">
        <img alt="" id="house" src="Pictures/sides/right.gif" style="z-index: 1; left: 372px;
            top: 219px; position: absolute; height: 138px; width: 120px" onclick="javascript:makeObj('Pictures/sides/sides-not-clicked.gif');" />
        </form>
    </body>
</html>

当前回答

不，你不能。只需在函数外部声明变量即可。你不必在赋值的同时声明它:

var trailimage;

function makeObj(address) {
  trailimage = [address, 50, 50];

2011-04-26 06:43:24

其他回答

只需在函数外部声明它，并在函数内部赋值即可。喜欢的东西:

<script type="text/javascript">
    var offsetfrommouse = [10, -20];
    var displayduration = 0;
    var obj_selected = 0;
    var trailimage = null ;  // Global variable
    function makeObj(address) {
        trailimage = [address, 50, 50];  // Assign value

或者简单地从函数内部的变量名中删除“var”也会使它成为全局的，但为了代码更干净，最好在外部声明一次。这也可以:

var offsetfrommouse = [10, -20];
var displayduration = 0;
var obj_selected = 0;

function makeObj(address) {
    trailimage = [address, 50, 50];  // Global variable, assign value

我希望这个例子能解释更多:http://jsfiddle.net/qCrGE/

var globalOne = 3;
testOne();

function testOne()
{
    globalOne += 2;
    alert("globalOne is :" + globalOne );
    globalOne += 1;
}

alert("outside globalOne is: " + globalOne);

testTwo();

function testTwo()
{
    globalTwo = 20;
    alert("globalTwo is " + globalTwo);
    globalTwo += 5;
}

alert("outside globalTwo is:" + globalTwo);

2011-04-26 06:41:33

只是声明

var trialImage;

在外面。然后

function makeObj(address) {
    trialImage = [address, 50, 50];
    ...
    ...
}

2011-04-26 06:41:40

全局变量在函数外部声明，以便在整个程序中访问，而局部变量存储在函数中，使用var，仅在该函数的作用域内使用。如果你声明一个变量没有使用var，即使它在函数中，它仍然会被视为全局变量。参考资料= https://www.freecodecamp.org/news/global-variables-in-javascript-explained/

2021-03-05 10:17:02

使用window对象不是一个好主意。正如我在评论中看到的，

'use strict';

function showMessage() {
    window.say_hello = 'hello!';
}

console.log(say_hello);

这将抛出一个使用say_hello变量的错误，我们需要首先调用showMessage函数。

2020-06-13 09:28:24

不，你不能。只需在函数外部声明变量即可。你不必在赋值的同时声明它:

var trailimage;

function makeObj(address) {
  trailimage = [address, 50, 50];

2011-04-26 06:43:24

在JavaScript函数中定义全局变量

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