The compiler will automatically supply the default argument value for the omitted argument.

编译器自动将默认实参的值提供给被忽略的实参。

youdao

The constructor examines each property in its parameters argument; for each one, if the property exists in the prototype, then its value overrides the parameter's default value.

构造方法在它的 parameters 参数中检查每个属性；对于每个属性，如果它存在于原型中，那么它的值覆盖参数的默认值。

youdao

Having two methods seems a bit wasteful. It would be nice if we could eliminate the second joiner method and declare that the separator argument in the first joiner has a default value.

写两个函数似乎有点浪费，如果我们能消除第二个joiner方法，在第一个jioner方法里为separator参数声明一个默认值，那就太好了。

youdao