CODEWITHSUNDEEP
javascript
R0b0tn1k
R0b0tn1k

Reputation: 4306

javascript: major slowdown in if case

I have a very simple code that generates a table.

However, when i added 3 if lines, it became super slow. Anyone have any ideas why?

Code:

for (var i=0; i<=noofRows; i++){
  var rg = genguid();
  for (var j=1; j<=noofbackuprows; j++){
  to+='<tr>';
  to+='<td>'  + prefix + rg + '-' + j;      
  to+='</td>';      
  if (j<3){var vval = 10000};
  if (j=3){var vval = 5000};
  if (j>4){var vval = 2500};
  to+='<td>'  + vval + '</td>';          
  to+='</tr>';      
    }
}

Infringing lines:

  if (j<3){var vval = 10000};
  if (j=3){var vval = 5000};
  if (j>4){var vval = 2500};

If i remove the infringing lines, it works great. What's going on?

Upvotes: 1

Views: 34

Answers (2)

Jamiec
Jamiec

Reputation: 136154

The reason is because in the loop you're setting j=3 for evermore. I'm surprised this does not crash the browser entirely.

Use the equality operator == or strict equality operator ===

Upvotes: 1

James Donnelly
James Donnelly

Reputation: 128786

Two problems with what you currently have:

if (j<3){var vval = 10000};
if (j=3){var vval = 5000};
if (j>4){var vval = 2500};

Firstly, j = 3 assigns the value 3 to j. It doesn't check to see whether j is equal to 3. To fix this, change this to == or ===:

if (j === 3) { var vval = 5000; }

This is why your application is becoming slow, because your for loop is getting stuck in a loop as after a certain point j will always be equal to 3.

Secondly, you should use else if, otherwise all three if statements will be checked even if the first one satisfied the requirement:

if (j < 3) { var vval = 10000 }
else if (j === 3) { var vval = 5000 }
else if (j > 4) { var vval = 2500 }

Also note that putting semicolons after the curly brackets on if statements is unnecessary, so I've removed those as well.

Upvotes: 3

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