为循环索引返回“[对象对象]-未定义”的Javascript
为循环索引返回“[对象对象]-未定义”的Javascript
提问于 2013-12-31 03:31:12
我试图对多个元素运行一个函数，所以我使用了for循环。我不明白为什么我没有得到任何价值。
var i;
var aFields = ["#business1A","#business1B","#business1C","#business1D","#business2A","#business2B","#business2C","#business2D",
"#business3A","#business3B","#business3C","#business3D","#business4A","#business4B","#business4C","#business4D",
"#business5A","#business5B","#business5C","#business5D","#business6A","#business6B","#business6C","#business6D"];
for (i = 0; i < aFields.length; i++) {
$(aFields[i]).keyup(function(){
alert($(aFields[i]+'Warning') + " - " +$(aFields[i]).val());
});
}回答 4
Stack Overflow用户
回答已采纳
发布于 2013-12-31 03:38:52
试试这个：
var i;
var aFields = ["#business1A","#business1B","#business1C","#business1D","#business2A","#business2B","#business2C","#business2D",
"#business3A","#business3B","#business3C","#business3D","#business4A","#business4B","#business4C","#business4D",
"#business5A","#business5B","#business5C","#business5D","#business6A","#business6B","#business6C","#business6D"];
for (i = 0; i < aFields.length; i++) {
(function(j){
$(aFields[j]).keyup(function(){
alert(($(this).attr('id')+'Warning') + " - " +$(this).val());
});
})(i);
}Stack Overflow用户
发布于 2013-12-31 03:35:45
这是因为在事件处理程序的回调函数中使用变量i。该事件发生在循环结束时，因此变量包含一个索引，该索引超出了数组中的最后一个项。
要使用绑定事件的迭代中的变量的值，可以通过创建作用域为每个迭代创建一个变量，使用立即执行的函数表达式：
var i;
var aFields = ["#business1A","#business1B","#business1C","#business1D","#business2A","#business2B","#business2C","#business2D",
"#business3A","#business3B","#business3C","#business3D","#business4A","#business4B","#business4C","#business4D",
"#business5A","#business5B","#business5C","#business5D","#business6A","#business6B","#business6C","#business6D"];
for (i = 0; i < aFields.length; i++) {
(function(j){
$(aFields[j]).keyup(function(){
alert($(aFields[j]+'Warning') + " - " +$(aFields[j]).val());
});
})(i);
}Stack Overflow用户
发布于 2013-12-31 03:33:42
这里的问题是闭包变量的错误使用 i，变量在所有密钥处理程序之间共享，所以当循环结束时，i将有值aFields.length，因此aFields[i]将返回未定义的值。
试一试
var aFields = ["#business1A", "#business1B", "#business1C", "#business1D", "#business2A", "#business2B", "#business2C", "#business2D",
"#business3A", "#business3B", "#business3C", "#business3D", "#business4A", "#business4B", "#business4C", "#business4D",
"#business5A", "#business5B", "#business5C", "#business5D", "#business6A", "#business6B", "#business6C", "#business6D"];
$.each(aFields, function (i, val) {
$(val).keyup(function () {
alert($(val + 'Warning') + " - " + $(val).val());
});
})页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/20851291
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