Javascript 如何使用默认值从对象中获取值
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How to get value from Object, with default value
提问by Jeremy S.
I constantly find myself passing config values to functions accessing them like this:
我经常发现自己将配置值传递给访问它们的函数，如下所示：
var arg1 = 'test1';
if(isUndefined(config.args.arg1)){
arg1 = config.args.arg1;
}
var arg2 = 'param2';
if(isUndefined(config.args.arg2)){
arg2 = config.args.arg2;
}
var arg3 = '123';
if(isUndefined(config.args.arg3)){
arg3 = config.args.arg3;
}
where I later use them like this:
我后来像这样使用它们：
var url = '<some-url>?id='+arg1+'&='+arg2 +'=' + arg3;
Does jQuery/ExtJS or any other framework provide a solution to access variables like this in a simple way, and give variables a default value?
jQuery/ExtJS 或任何其他框架是否提供了一种解决方案来以简单的方式访问这样的变量，并为变量提供默认值？
Something like:
就像是：
getValueOfObject(config,'args.arg3','<default>');
Or is there maybe a standard solution for this.
或者是否有一个标准的解决方案。
NOTE:
笔记：
I was also thinking about the common pattern where you have defaults
我也在考虑你有默认值的常见模式
var defaults = {
args: {
args1: ....
}
...
}
and doing an object merge.
并进行对象合并。
And then encoding the object to a param String. But as you can see the object valuesalso sometimes contain parameter names.
然后将对象编码为参数字符串。但是正如您所看到的，对象值有时也包含参数名称。
回答by karim79
Generally, one can use the or operatorto assign a default when some variable evaluates to falsy:
通常，当某个变量的计算结果为假时，可以使用or 运算符来分配默认值：
var foo = couldBeUndefined || "some default";
so:
所以：
var arg1 = config.args.arg1 || "test";
var arg2 = config.args.arg2 || "param2";
assuming that config.argsis always defined, as your example code implies.
假设config.args始终定义，正如您的示例代码所暗示的那样。
回答by Raynos
try var options = extend(defaults, userOptions);
尝试 var options = extend(defaults, userOptions);
This way you get all the userOptions and fall back to defaults when they don't pass any options.
通过这种方式，您可以获得所有 userOptions 并在它们不传递任何选项时回退到默认值。
Note use any extendimplementation you want.
请注意使用extend您想要的任何实现。
