在javascript中，如何区分没有arg传递和未定义的arg传递(in javascript, how to distinguish between no arg passed and undefined arg passed)

 在一个函数中，如何识别非arg和未定义的arg？ 
 
myFunc( 'first' );

var obj = { a: 123 };
myFunc( 'first', obj.b );
_or_
myFunc( 'first', undefined )
 
 
  
  arguments.length指的是通过命名参数的参数，所以它没有帮助 
 可以用arguments.length轻松解决 - 抱歉大脑放屁！ 
 
function myFunc( a, b ) {

  // Case A: if no second arg, provide one
  // should be: if( arguments.length < 2 ) ...
  if( b === undefined ) b = anotherFunc;

  // Case B: if b is not resolved - passed but undefined, throw
  else if( b === undefined ) throw( 'INTERNAL ERROR: undefined passed' );

  // Case C: if b not a function, resolve by name
  else if( typeof b != 'function' ) { ... }

  ...
}
 
 在myFunc捕获案例A和案例B的正确方法是什么？ 

within a function, how to discern between a non-arg and an undefined arg?
 
myFunc( 'first' );

var obj = { a: 123 };
myFunc( 'first', obj.b );
_or_
myFunc( 'first', undefined )
 
 
  
  arguments.length refers to arguments 
  past the named arguments, so it's no help 
  Can be solved easily with arguments.length - sorry about the brain fart!
 
function myFunc( a, b ) {

  // Case A: if no second arg, provide one
  // should be: if( arguments.length < 2 ) ...
  if( b === undefined ) b = anotherFunc;

  // Case B: if b is not resolved - passed but undefined, throw
  else if( b === undefined ) throw( 'INTERNAL ERROR: undefined passed' );

  // Case C: if b not a function, resolve by name
  else if( typeof b != 'function' ) { ... }

  ...
}
 
What is the correct way to capture Case A and Case B in myFunc?

原文：https://stackoverflow.com/questions/7750577