javascript using a condition in switch case

Question

Sorry for that dumb question  How can I use a condition for a case in the javascript switch-case language element  Like in the example below  a case should match when the variable liCount is  lt  5 and  0  however  my code does not work   switch  liCount        case 0          setLayoutState  start            var api       UploadList   data  jsp            api reinitialise            break      case  liCount lt  5  amp  amp  liCount gt 0           setLayoutState  upload1Row            var api       UploadList   data  jsp            api reinitialise            break      case  liCount lt  10  amp  amp  liCount gt 5           setLayoutState  upload2Rows            var api       UploadList   data  jsp            api reinitialise            break      case  liCount gt 10           var api       UploadList   data  jsp            api reinitialise            break                        Thanks for any advice

User · Answer

You ve way overcomplicated that  Write it with if statements instead like this       if liCount    0      setLayoutState  start    else if liCount lt  5      setLayoutState  upload1Row    else if liCount lt  10      setLayoutState  upload2Rows         UploadList   data  jsp   reinitialise      Or  if ChaosPandion is trying to optimize as much as possible   setLayoutState liCount    0    start                   liCount  lt   5    upload1Row                   liCount  lt   10    upload2Rows                   null        UploadList   data  jsp   reinitialise

User · Answer

You want to use if statements   if  liCount     0        setLayoutState  start      else if  liCount  lt   5        setLayoutState  upload1Row      else if  liCount  lt   10        setLayoutState  upload2Rows          UploadList   data  jsp   reinitialise

User · Answer

Your code does not work because it is not doing what you are expecting it to do   Switch blocks take in a value  and compare each case to the given value  looking for equality   Your comparison value is an integer  but most of your case expressions resolve to a boolean value   So  for example  say liCount   2   Your first case will not match  because 2    0   Your second case   liCount lt  5  amp  amp  liCount gt 0  evaluates to true  but 2    true  so this case will not match either   For this reason  as many others have said  you should use a series of if   then   else if blocks to do this

User · Answer

switch  true      case condition0              break    case condition1              break      will work in JavaScript as long as your conditions return proper boolean values  but it doesn t have many advantages over else if statements

User · Answer

You can use fall-through method in switch case  const x    Welcome    switch  x      case  Come       console log 1      break     case  Welcome     case  Wel     case  come       console log 2      break     case  Wel       console log 3      break     default      break           gt  Result   gt  2

User · Answer

See dmp s answer below   I d delete this answer if I could  but it was accepted so this is the next best thing     You can t   JS Interpreters require you to compare against the switch statement  e g  there is no  case when  statement    If you really want to do this  you can just make if         else if         blocks

User · Answer

That s a case where you should use if clauses

User · Answer

if the possible values are integers you can bunch up cases  Otherwise  use ifs   var api  tem   switch liCount       case 0      tem   start       break      case 1  case 2  case 3  case 4  case 5      tem   upload1Row       break      case 6  case 7  case 8  case 9  case 10      tem   upload2Rows       break      default      break    if tem  setLayoutState  tem   api      UploadList   data  jsp    api reinitialise

User · Answer

Although in the particular example of the OP s question  switch is not appropriate  there is an example where switch is still appropriate beneficial  but other evaluation expressions are also required  This can be achieved by using the default clause for the expressions   switch  foo      case  bar          do something     break    case  foo          do something     break           other plain comparison cases   default      if  foo length  gt  16             something specific       else if  foo length  lt  2             maybe error       else            default action for everything else

User · Answer

This works   switch  true        case liCount    0          setLayoutState  start            var api       UploadList   data  jsp            api reinitialise            break      case liCount lt  5  amp  amp  liCount gt 0          setLayoutState  upload1Row            var api       UploadList   data  jsp            api reinitialise            break      case liCount lt  10  amp  amp  liCount gt 5          setLayoutState  upload2Rows            var api       UploadList   data  jsp            api reinitialise            break      case liCount gt 10          var api       UploadList   data  jsp            api reinitialise            break                        A previous version of this answer considered the parentheses to be the culprit  In truth  the parentheses are irrelevant here - the only thing necessary is switch true       and for your case expressions to evaluate to booleans   It works because  the value we give to the switch is used as the basis to compare against  Consequently  the case expressions  also evaluating to booleans will determine which case is run  Could also turn this around  and pass switch false      and have the desired expressions evaluate to false instead of true   but personally prefer dealing with conditions that evaluate to truthyness  However  it does work too  so worth keeping in mind to understand what it is doing    Eg  if liCount is 3  the first comparison is true      liCount    0   meaning the first case is false  The switch then moves on to the next case true      liCount lt  5  amp  amp  liCount gt 0   This expression evaluates to true  meaning this case is run  and terminates at the break  I ve added parentheses here to make it clearer  but they are optional  depending on the complexity of your expression    It s pretty simple  and a neat way  if it fits with what you are trying to do  of handling a long series of conditions  where perhaps a long series of   f       else if       else if        might introduce a lot of visual noise or fragility    Use with caution  because it is a non-standard pattern  despite being valid code

User · Answer

If that s what you want to do  it would be better to use if statements   For example   if liCount    0       setLayoutState  start      if liCount lt  5  amp  amp  liCount gt 0       setLayoutState  upload1Row      if liCount lt  10  amp  amp  liCount gt 5       setLayoutState  upload2Rows                   var api       UploadList   data  jsp        api reinitialise

User · Answer

Notice that we don t pass score to the switch but true  The value we give to the switch is used as the basis to compare against   The below example shows how we can add conditions in the case  without any if statements   function getGrade score        let grade         Write your code here     switch true            case score  gt   0  amp  amp  score  lt   5          grade    F           break          case score  gt  5  amp  amp  score  lt   10          grade    E           break          case score  gt  10  amp  amp  score  lt   15          grade    D           break          case score  gt  15  amp  amp  score  lt   20          grade    C           break          case score  gt  20  amp  amp  score  lt   25          grade    B           break          case score  gt  25  amp  amp  score  lt   30          grade    A           break             return grade

[javascript] javascript: using a condition in switch case

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