if(!var_name)

[alzami]

what is the actual meaning of these statement

#if(!var_name)

#if(var_name)

[Ingolme]

They're equivalent to

if(var_name == false)

and

if(var_name == true)

[alzami]

in this example what is the use of the variable (timer_is_on)?

http://www.w3schools.com/jsref/tryit.asp?filename=tryjsref_win_settimeout_cleartimeout2

it is not even needed here.

what is the use of If(!timer_is_on) in the function startcount()??

Edited December 24, 2013 by alzami

[Hadien]

whats happening is that the if() syntax is casting timer_is_on from a number to a boolean. any number other than 0 is considered true. the "!" is a not operator so when javascript sees "if(!timer_is_on)", its roughly translating to "if timer_is_on is NOT 0, then do this stuff"

 

its important that the function made that check so that it didn't make multiple setTimeout function calls. if it did then the id of the previous setTimeout would be lost, overwritten with the new setTimeout function. If that happened then there would be no way to use clearTimeout on the first setTimeout.

 

actually…. after calling stopCount, one of the setTimeouts would clear and then you would be able to stop the 2nd timeout after its made a count, however, that wouldn't be desired functionality and would be confusing.

[alzami]

thanks!what actually cofused me is i removed the timer_is_on var from the editor and codes worked fine.so i wonder why use an extra var when it is not necessary!!