如何在循环中使用switch语句？

Question

 for(var i=0; i<20; i++) { if(i%3===0) { console.log(i, 'Foo') } else { console.log(i, 'Default') } } 

Now, I wonder how can we write the code using switch statement inside the loop:

 for(var i=0; i<20; i++) { switch(i) { case (i%3===0): console.log(i,'Foo') break default: console.log(i,'Default') break } } 

But it results 'Default' always. I have tried using label, anonymous function, etc. but not able to output like if condition. Am I doing something wrong with the switch statment?

Edit:

I was trying to do like this in fact:

case (i%3===0):
   console.log(i,'Foo')
   break
case (i%5===0):
   console.log(i,'Bar')
   break

Answer 1

You are trying to use a switch statement like a series of if and else if statements. A switch statement does not work that way. The first case that matches the value of the variable that is in the switch statement will be evaluated. You can use switch(true) so the first case that is true will be evaluated.

 for(var i=0; i<20; i++) { switch(true) { case (i%3===0)://if console.log(i,'Foo') break case (i%5===0)://else if console.log(i,'Bar') break default://else console.log(i,'Default') break } } 

Otherwise, you need to switch the value of i modulo 3 (if it equals zero then it is divisible by 3 ).

 for(var i=0; i<20; i++) { switch(i%3) { case (0): console.log(i,'Foo') break default: console.log(i,'Default') break } } 

However, a switch statement generally should not be used in this case. You should just go with a series of if (and else if statements).

 for(var i=0; i<20; i++) { if(i%3==0){ console.log(i, 'Foo'); } else if(i%5==0){ console.log(i, 'Bar'); } else { console.log(i, 'Default'); } } 

Answer 2

You can take the value of i%3 in a variable and use that in switch-case because the case evaluates a constant or expression.

 for(var i=0; i<20; i++) { var val = i%3; switch(val) { case 0: console.log(i,'Foo') break; default: console.log(i,'Default') } } 

Answer 3

You should switch the expression you want to check against, in this case that's i%3 and than make cases for what that expression might be, eg case 0: , case 1: and so on:

 for(var i=0; i<20; i++) { switch(i%3) { case 0: console.log(i,'Foo') break; case 1: console.log(i,'Bar') default: console.log(i,'Default') } } 

Answer 4

try this - with the %3 moved

 for(var i=0; i<20; i++) { switch(i%3) { case 0: console.log(i,'Foo') break; default: console.log(i,'Default') break; } }