Javascript简写

Question

If I can say:

var big = (x > 10) ? true : false;

instead of:

var big;
if (x > 10) {
    big = true;
}
else {
    big = false;
}

how do I make this similarly shorter?

var now = new Date

if (now.getHours() < 5) {
    return "late night pick me up";
}
else if (now.getHours() < 9) {
    return "breakfast";
}
else if (now.getHours() < 13) {
    return "lunch";
}
else if (now.getHours() < 17) {
    return "afternoon snak";
}
else {
    return "dinner";
}

Thanks a big bunch!

Answer 1

var now = new Date().getHours();

return now < 5 ? "late night pick me up" :
       now < 9 ? "breakfast" :
       now < 13 ? "lunch" :
       now < 17 ? "afternoon snak" : "dinner";

Answer 2

You can't, without a bunch of messy nested ternary operators. The ternary operator is only good for one liners.

Answer 3

You can't shorthand that particularly, personally I would just write it like this:

if (now.getHours() < 5) return "late night pick me up";
else if (now.getHours() < 9) return "breakfast";
else if (now.getHours() < 13) return "lunch";
else if (now.getHours() < 17) return "afternoon snak";
else return "dinner";

That's not too bad is it?

Answer 4

You probably don't want to, as arguably it would be less readable. However, you could simply nest the ternary operator like so:

var now = (now.getHours() < 5) ? "late night pick me up" : ((now.getHours() < 9) ? "breakfast" : ((now.getHours() < 13) ? "lunch" : ((now.getHours() < 17) ? "afternoon snack" : "dinner")))));

I hope you can see why this isn't a good idea!

A longer, more complex condition like this generally needs multiple lines and good block separation to be easily understandable - and while you could arguably add line breaks, the standard if-else blocks are ultimately going to come out the winner at clearly expressing your intent.

Answer 5

First, try var big = x > 10; instead of var big = (x > 10) ? true : false; var big = (x > 10) ? true : false;

Second, you don't need if-else when you have return.

//looks  a little confusing, but you can move the return to line after ifs
var now = new Date  
if (now.getHours() < 5)  return "late night pick me up"; 
if (now.getHours() < 9)  return "breakfast";
if (now.getHours() < 13) return "lunch";
if (now.getHours() < 17) return "afternoon snak";
return "dinner"; 

Answer 6

I stumbled across this in search for something else. Here's a little shorthand trick using logical operators and abusing the fact string literals are truthy =]

var hr = new Date().getHours();

return hr < 5 && 'late night pick me up' 
    || hr < 9 && 'breakfast' 
    || hr < 13 && 'lunch' 
    || hr < 17 && 'afternoon snack' 
    || 'dinner';

Answer 7

It will look quite messy:

return ((now.getHours() < 5)?"late night pick me up":
         ((now.getHours() < 9)?"breakfast":
            ((now.getHours() < 13)?"lunch":
               ((now.getHours() < 17)?"afternoon snack":
                  "dinner"
               )
            )
          )
       );

You have to remember to match parenthesis.

Answer 8

You could always use a switch statement:

switch(true)
{
case (now.getHours() < 5):
  return "late night pick me up";
  break;
case (now.getHours() < 9):
  return "breakfast";
  break;  //etc...
default:
  return "dinner";
}

Answer 9

You can always use a table to replicate functionality:

var now = new Date();
var meals = [
    "late night pick me up",
    "breakfast",
    "lunch",
    "afernoon snack",
    "dinner"];
return meals[parseInt(now.getHours()-4)/4];