Dynamically change the condition in if statement in javascript

Question

This code is to dynamiclly change the condition , however, this statement is recognized and interperted by chrome but not fx , how to fix the problem ? thanks

if a % 2 == 0 
  var condition = b == c  || b == d;
else 
  var condition = b == e  || b == f ;

if (condition)
  ......

Any variable declared as var someVar will be hoisted to the top of the scope, so you only need to use the var keyword once per symbol. — Evan Davis
– Evan Davis, Commented Feb 3, 2013 at 14:13
This code should work fine in Firefox. Can you link to a testcase that doesn't work? — Boris Zbarsky
– Boris Zbarsky, Commented Feb 3, 2013 at 18:07

salexch · Accepted Answer · 2013-02-03 13:41:23Z

4

var condition = (a % 2 == 0) ? (b == c  || b == d) : (b == e  || b == f);

answered Feb 3, 2013 at 13:41

salexch

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Comments

Knerd · Accepted Answer · 2013-02-03 13:53:15Z

0

Write it like this:

var condition;
if (a % 2 == 0)
    condition = b == c  || b == d;
else 
    condition = b == e  || b == f ;

if (condition)
   ......

edited Feb 3, 2013 at 13:53

answered Feb 3, 2013 at 13:41

Knerd

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11 Comments

Knerd Over a year ago

Because you got condition definied before you use it.

NedStarkOfWinterfell Over a year ago

What purpose will that serve? It's an if-else conditional, either the if or the else will execute, so the variable gets defined inside one of them anyway...

Knerd Over a year ago

I can tell how it is in C#, C++ and Java, when you want to use a variable out of an if else statement you have to define it before you use it.

NedStarkOfWinterfell Over a year ago

But not in Javasript. In JS, a variable declared with var will always be pre-initialized with undefined, so even if the conditional doesn't evaluate to true and the variable never gets the chance to be given the supposed value, because the code never enters that unit, outside that unit, it's value will be undefined...

Evan Davis Over a year ago

This actually isn't a bad answer, even though you didn't know why it is or isn't the right answer.

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