Javascript：最有效的方法是将变量定义为函数调用，或者将null定义为变量？

Question

Using ternary operator requires two calls to the function.

var colour = (tryAdventurousColour() != null) ? tryAdventurousColour() : 'black';

Possible to do it in 1 line?

EDIT: Fixed syntax EDIT: Like this but better

var colour = ( (colour = tryAdventurousColour() ) != null ) ? colour : 'black';

Answer 1

Use JavaScript's logical or operator:

var colour = tryAdventurousColour() || 'black';

Your function tryAdventurousColour() will be executed once. If it returns a "truthy" value then that colour variable will be assigned to that value, otherwise colour will be 'black'. This fits your scenario perfectly since null is a "falsy" value.

In more general terms, the expression a || b a || b returns a if it can be converted to true (is "truthy"), otherwise it returns b . Note that non-zero numbers, non-empty strings and objects will all be converted to true. null , undefined, 0, "" will all be converted to false. (I'm sure somebody will correct me if I've left something out.)

Answer 2

 var colour = (tryAdventurousColour()) ? tryAdventurousColour() : 'black';