unable to understand working of this function

Question

To check weather the element is exist or not I am using

   if($('#id').length)
       //statement 1
   else
      //statement 2

It is working fine for me. But statement1 will execute when the condition is true otherwise statement2 will execute. But how is it working when length is returning length (it is a number like 1 , 2...)

I thought if the length is 0, then it is taking false for 0. But what about remaining cases. I am unable to understand what is happening here. Thanks in advance...

I think $('#id').length returns a string. Try praseInt() on the result.... — Jay Bhatt, Apr 19 '13 at 08:08
why downvote .Please leave a comment before giving a downvote — PSR, Apr 19 '13 at 08:18

score 3 · Accepted Answer · answered Apr 19 '13 at 08:06

From the MDN on if :

Any value that is not undefined, null, 0, NaN, or the empty string (""), and any object, including a Boolean object whose value is false, evaluates to true when passed to a conditional statement

This means that when the length is 1 (or greater but that can't happen for this selector) then it evaluates to true.

So when the element with id id is found, the statement 1 is executed. when the length is 0, then statement 2 is executed.

h2ooooooo · Answer 2 · 2013-04-19T08:14:36.253

Here's some output from the chrome console, that might help you:

> Boolean(1) //The number 1
true

> Boolean(0) //The number 0
false

> Boolean(0.0000000000000000000000000000000000000000001) //A very close to 0 float
true

> Boolean(0.000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001) //This is where it starts rounding down to zero
false

> Boolean(false) //A boolean "false"
false

> Boolean(NaN) //Not a number
false

> Boolean(undefined) //Undefined
false

> Boolean("") //An empty string
false

> Boolean(-3) //A negative number
true

> Boolean("string") //A string that is not empty
true

> Boolean([]) //An empty array
true

> Boolean({}) //An empty object
true

> Boolean(2.5) //A float
true

..hence, if length is 0 (as in; the element could not be found) then it does not evaluate to true and therefore chooses the } else { statement instead.

score 0 · Answer 3 · answered Apr 19 '13 at 08:07

Javascript has a concept of truthy/falsy where values like 0, false, undefined and null are considered to be falsy and others are considered to be truthy.

If if the length is 0 then it becomes falsy and the condition will fail, else if length !=0 then the value is considered to be truthy and the condition will succeed.

score -1 · Answer 4 · edited May 23 '17 at 11:43

-1

Yes this is how javascript works

An explanation here

In JavaScript, why is "0" equal to false, but when tested by 'if' it is not false by itself?

edited May 23 '17 at 11:43

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answered Apr 19 '13 at 08:08

ripu1581

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unable to understand working of this function

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