How can I use goto in Javascript

Question

I have some code that I absolutely must implement using goto  For example  I want to write a program like this   start  alert  RINSE    alert  LATHER    repeat  goto start   Is there a way to do that in Javascript

User · Answer

In classic JavaScript you need to use do-while loops to achieve this type of code. I presume you are maybe generating code for some other thing.

The way to do it, like for backending bytecode to JavaScript is to wrap every label target in a "labelled" do-while.

LABEL1: do {
  x = x + 2;
  ...
  // JUMP TO THE END OF THE DO-WHILE - A FORWARDS GOTO
  if (x < 100) break LABEL1;
  // JUMP TO THE START OF THE DO WHILE - A BACKWARDS GOTO...
  if (x < 100) continue LABEL1;
} while(0);

Every labelled do-while loop you use like this actually creates the two label points for the one label. One at the the top and one at the end of the loop. Jumping back uses continue and jumping forwards uses break.

// NORMAL CODE

MYLOOP:
  DoStuff();
  x = x + 1;
  if (x > 100) goto DONE_LOOP;
  GOTO MYLOOP;


// JAVASCRIPT STYLE
MYLOOP: do {
  DoStuff();
  x = x + 1;
  if (x > 100) break MYLOOP;
  continue MYLOOP;// Not necessary since you can just put do {} while (1) but it     illustrates
} while (0)

Unfortunately there is no other way to do it.

Normal Example Code:

while (x < 10 && Ok) {
  z = 0;
  while (z < 10) {
    if (!DoStuff()) {
      Ok = FALSE;
      break;
    }
    z++;
  }
  x++;
}

So say the code gets encoded to bytecodes so now you must put the bytecodes into JavaScript to simulate your backend for some purpose.

JavaScript style:

LOOP1: do {
  if (x >= 10) break LOOP1;
  if (!Ok) break LOOP1;
  z = 0;
  LOOP2: do {
    if (z >= 10) break LOOP2;
    if (!DoStuff()) {
      Ok = FALSE;
      break LOOP2;
    }
    z++;
  } while (1);// Note While (1) I can just skip saying continue LOOP2!
  x++;
  continue LOOP1;// Again can skip this line and just say do {} while (1)
} while(0)

So using this technique does the job fine for simple purposes. Other than that not much else you can do.

For normal Javacript you should not need to use goto ever, so you should probably avoid this technique here unless you are specificaly translating other style code to run on JavaScript. I assume that is how they get the Linux kernel to boot in JavaScript for example.

NOTE! This is all naive explanation. For proper Js backend of bytecodes also consider examining the loops before outputting the code. Many simple while loops can be detected as such and then you can rather use loops instead of goto.

User · Answer

You should probably read some JS tutorials like this one   Not sure if goto exists in JS at all  but  either way  it encourages bad coding style and should be avoided   You could do   while   some condition        alert  RINSE        alert  LATHER

User · Answer

const     start   0      more   1      pass   2      loop   3      skip   4      done   5   var label   start    while  true       var goTo   null      switch  label           case start              console log  start            case more              console log  more            case pass              console log  pass            case loop              console log  loop                goTo   pass  break          case skip              console log  skip            case done              console log  done               if  goTo    null  break      label   goTo

User · Answer

goto begin and end of all parents closures  var foo false  var loop1 true  LABEL1  do  var LABEL1GOTO false      console log  here be 2 times        if  foo  false           foo true          LABEL1GOTO true continue LABEL1    goto up      else          break LABEL1    goto down           console log  newer go here      while LABEL1GOTO

User · Answer

example of goto in javascript   var i  j  loop 1      for  i   0  i  lt  3  i        The first for statement is labeled  loop 1          loop 2              for  j   0  j  lt  3  j        The second for statement is labeled  loop 2                  if  i     1  amp  amp  j     1                        continue loop 1                                    console log  i       i      j       j

User · Answer

To achieve goto-like functionality while keeping the call stack clean  I am using this method      in other languages     tag1     doSomething       tag2     doMoreThings       if  someCondition  goto tag1     if  otherCondition  goto tag2   function tag1         doSomething        setTimeout tag2  0      optional  alternatively just tag2       function tag2         doMoreThings        if  someCondition            setTimeout tag1  0      those 2 lines         return                  imitate goto           if  otherCondition            setTimeout tag2  0      those 2 lines         return                  imitate goto           setTimeout tag3  0      optional  alternatively just tag3                Please note that this code is slow since the function calls are added to timeouts queue  which is evaluated later  in browser s update loop   Please also note that you can pass arguments  using setTimeout func  0  arg1  args     in browser newer than IE9  or setTimeout function   func arg1  args       0  in older browsers   AFAIK  you shouldn t ever run into a case that requires this method unless you need to pause a non-parallelable loop in an environment without async await support

User · Answer

You can simple use a function   function hello         alert  RINSE        alert  LATHER        hello

User · Answer

Generally  I d prefer not using GoTo for bad readability  To me  it s a bad excuse for programming simple iterative functions instead of having to program recursive functions  or even better  if things like a Stack Overflow is feared   their true iterative alternatives  which may sometimes be complex    Something like this would do   while true       alert  RINSE       alert  LATHER        That right there is an infinite loop  The expression   true   inside the parantheses of the while clause is what the Javascript engine will check for - and if the expression is true  it ll keep the loop running  Writing  true  here always evaluates to true  hence an infinite loop

User · Answer

Actually  I see that ECMAScript  JavaScript  DOES INDEED have a goto statement  However  the JavaScript goto has two flavors    The two JavaScript flavors of goto are called labeled continue and labeled break  There is no keyword  goto  in JavaScript  The goto is accomplished in JavaScript using the break and continue keywords   And this is more or less explicitly stated on the w3schools website here http   www w3schools com js js switch asp    I find the documentation of the labeled continue and labeled break somewhat awkwardly expressed   The difference between the labeled continue and labeled break is where they may be used  The labeled continue can only be used inside a while loop  See w3schools for some more information                Another approach that will work is to have a giant while statement with a giant switch statement inside   while  true        switch  goto variable                case 1                 some code             goto variable   2             break          case 2              goto variable   5      case in etc  below             break          case 3              goto variable   1             break            etc

User · Answer

Another alternative way to achieve the same is to use the tail calls  But  we don   t have anything like that in JavaScript  So generally  the goto is accomplished in JS using the below two keywords  break and continue  reference  Goto Statement in JavaScript  Here is an example   var number   0  start position  while true    document write  Anything you want to print    number    if number  lt  100  continue start position  break

User · Answer

No  They did not include that in ECMAScript      ECMAScript has no goto statement

User · Answer

Sure  using the switch construct you can simulate goto in JavaScript  Unfortunately  the language doesn t provide goto  but this is a good enough of a replacement   let counter   10 function goto newValue      counter   newValue   while  true      switch  counter        case 10  alert  RINSE       case 20  alert  LATHER       case 30  goto 10   break

User · Answer

This is an old question  but since JavaScript is a moving target - it is possible in ES6 on implementation that support proper tail calls  On implementations with support for proper tail calls  you can have an unbounded number of active tail calls  i e  tail calls doesn t  grow the stack     A goto can be thought of as a tail call with no parameters   The example   start  alert  RINSE           alert  LATHER           goto start   can be written as   function start     alert  RINSE                        alert  LATHER                        return start       Here the call to start is in tail position  so there will be no stack overflows   Here is a more complex example    label1    A            B            if C goto label3            D  label3    E            goto label1   First  we split the source up into blocks  Each label indicates the start of a new block     Block1      label1    A                B                if C goto label3                D    Block2          label3    E                goto label1   We need to bind the blocks together using gotos   In the example the block E follows D  so we add a goto label3 after D    Block1      label1    A                B                if C goto label2                D                goto label2    Block2          label2    E                goto label1   Now each block becomes a function and each goto becomes a tail call    function label1                    A                B                if C then return  label2                    D                return  label2          function label2                    E                return  label1          To start the program  use label1     The rewrite is purely mechanical and can thus be done with a macro system such as sweet js if need be

User · Answer

Absolutely  There is a project called Summer of Goto that allows you use JavaScript at its fullest potential and will revolutionize the way you can write your code  This JavaScript preprocessing tool allows you to create a label and then goto it using this syntax   lbl   lt label-name gt  goto  lt label-name gt   For example  the example in the question can be written as follows   lbl  start  alert  quot LATHER quot    alert  quot RINSE quot     lbl  repeat  goto start   Note that you are not just limited to simple trivial programs like an endless LATHER RINSE repeat cycle   the possibilities afforded by goto are endless and you can even make a Hello  world  message to the JavaScript console 538 times  like this  var i   0   lbl  start  console log  quot Hello  world  quot    i    if i  lt  538  goto start   You can read more about how goto is implemented  but basically  it does some JavaScript preprocessing that takes advantage of the fact that you can simulate a goto with a labelled while loop  So  when you write the  quot Hello  world  quot  program above  it gets translated to something like this  var i   0  start  while true      console log  quot Hello  world  quot      i      if i  lt  538  continue start    break     There are some limitations to this preprocessing process  because while loops cannot stretch across multiple functions or blocks  That s not a big deal  though   I m sure the benefits of being able to take advantage of goto in JavaScript will absolutely overwhelm you  All above link that lead to goto js library is ALL DEAD  here is links needed  goto js  uncompressed  --- parseScripts js  uncompressed  From Goto js   P S  For anyone who is wondering  so far a total of zero people   Summer of Goto is a term that was popularized by Paul Irish  while discussing this script and PHP   s decision to add goto into their language  And for those who do not immediately recognize that this entire thing is a joke  please forgive me   lt     insurance

User · Answer

There is a way this can be done  but it needs to be planned carefully  Take for example the following QBASIC program   1 A   1  B   10  10 print  A     A  20 IF  A  lt  B  THEN A   A   1  GOTO 10 30 PRINT  That s the end     Then create your JavaScript to initialize all variables first  followed by making an initial function call to start the ball rolling  we execute this initial function call at the end   and set up functions for every set of lines that you know will be executed in the one unit   Follow this with the initial function call     var a  b  function fa        a   1      b   10      fb      function fb        document write  a      a     lt br gt         fc      function fc        if a lt b           a            fb            return            else           document write  That s the end  lt br gt             fa      The result in this instance is   a   1 a   2 a   3 a   4 a   5 a   6 a   7 a   8 a   9 a   10 That s the end

User · Answer

How about a for loop   Repeat as many times as you like   Or a while loop  repeat until a condition is met   There are control structures that will let you repeat code   I remember GOTO in Basic    it made such bad code   Modern programming languages give you better options that you can actually maintain

[javascript] How can I use goto in Javascript?

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