Javascript/Jquery - 在函数中设置默认值
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Javascript/Jquery - Setting default value in function
提问by John
Using javascript/jquery is there a way to set a variable to a default value if no value is passed in the function? For example
如果函数中没有传递值，是否可以使用 javascript/jquery 将变量设置为默认值？例如
function someFunction(data1,data2)
{
}
If data1 or data 2 is empty it gives me an undefined value. In php I could do just this:
如果 data1 或 data 2 为空，它会给我一个未定义的值。在 php 中，我可以这样做：
function somefunction(data1 = '',data2 = '')
{
}
So if no variable is passed or data1 or data 2 it defaults to ''. In JS/Jquery do I have to check if there is a value and set it accordingly?
因此，如果没有传递变量或 data1 或 data 2，则默认为 ''。在 JS/Jquery 中，我是否必须检查是否有值并相应地设置它？
function someFunction(data1,data2)
{
if(!data1) {
data1 = '';
}
if(!data2) {
data2 = ''
}
}
Just seems alot needs to be done to check if variable is empty or not to give it a default value.
似乎需要做很多事情来检查变量是否为空或不给它一个默认值。
回答by Amber
function foo(bar) {
bar = bar || 'default';
}
(Alternatively, if you only ever use baronce, you can just replace that usage with bar || <default value>and skip the intermediate assignment.)
（或者，如果您只使用bar一次，您可以只用替换该用法bar || <default value>并跳过中间分配。）
回答by Christian P
function someFunction(data){
data = data || 'my value';
}
The only problem with this is that the 0, falseand undefinedare treated the same:
唯一的问题是0,false和undefined的处理方式相同：
someFunction(1); // data = 1;
someFunction(-1); // data = -1;
someFunction(); // data = 'my value';
someFunction(0); // data = 'my value';
someFunction(false); // data = 'my value';
回答by Maurizio In denmark
You can use this:
你可以使用这个：
function foo(optionalArg) {
optionalArg = optionalArg|| 'defaultValue';
}
as long as you never pass a value to the parameter. This logic fails if optionalArg is passed Try this instead:
只要您从不向参数传递值。如果传递 optionalArg 则此逻辑失败 试试这个：
function foo(optionalArg) {
optionalArg = (typeof optionalArg === "undefined") ? "defaultValue" : optionalArg;
}
回答by Deeptechtons
You would use jquery's extend method but define defaults in the code like below
您将使用 jquery 的扩展方法，但在代码中定义默认值，如下所示
$.fn.myPlugin = function (settings) {
var options = jQuery.extend({
name: "MyPlugin",
target: document,
onOpen: function () {},
onClose: function () {},
onSelect: function () {}
}, settings);
}
now you could do
现在你可以做
$("#divId").myPlugin({
target: $("#div2")
};
this will now override the documenttarget defined inside the defaults with element having div2 as id.
这现在将document使用 element覆盖默认值中定义的目标having div2 as id。
