JavaScript Unexpected end of input with a break

Question

With this very simple code:

<body>
<script>
  var j;
  j=0;
  do {
    document.write("J="+j+" ");
    j++;
    if (j=4) {
      break;
    }
  }
</script>
</body>

I get an error: Uncaught SyntaxError: Unexpected end of input just at the end of the script. This happens since I'm trying to use break to jump out from the loop.

Of course this is not the code I'm working on, which is way more complicated and needs the break jump. I know in this case a do while loop or for loop would have made it. This is just the smallest code I have showing the error.

Parentheses are balanced, braces are balanced, why does it say it is incomplete?

P.S. I have also tried this very same code as a function, receiving the error Uncaught SyntaxError: Unexpected token } on the brace that closes the function.

See answer below. Also, if (j=4) { should be if (j==4) {... = is assignment where as == comparison. — Adrian
– Adrian, Commented Apr 9, 2019 at 15:55
Yes, thanks. The = Vs. == point get obscured for me 'thanks' to the greater issue of the code not running. JS not my native language. — Envite
– Envite, Commented Apr 9, 2019 at 16:03

junvar · Accepted Answer · 2019-04-09 15:55:02Z

3

do statements in Javascript expect a corresponding while expression.

E.g.

  var j;
  j=0;
  do {
    document.write("J="+j+" ");
    j++;
    if (j=4) {
      break;
    }
  } while (true);

Also worth noting, if (j=4) is always true in JS, you probably meant === for comparison instead of = for assignment. (as Adriani6 mentioned in the comments)

Though, if this is the complete example you're working with, then it would be cleaner to remove the if condition and break as such:

  var j;
  j=0;
  do {
    document.write("J="+j+" ");
    j++;
  } while (j !== 4);

or even easier to read:

for (let j = 0; j < 4; j++) {
   document.write("J="+j+" ");
}

answered Apr 9, 2019 at 15:55

junvar

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1 Comment

Envite Over a year ago

I already said this is not the complete code I'm working on, so the latter codes don't help me (to my real problem), but It seems you made the point. Thanks.

Arm144 · Accepted Answer · 2019-04-09 15:59:28Z

0

if (j=4) {
      break;
    }

it should be j==4

answered Apr 9, 2019 at 15:59

Arm144

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2 Comments

chevybow Over a year ago

Should actually be j === 4 ;)

Arm144 Over a year ago

Well yes is more restrictive, also compares the type

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