Difference between setTimeout with and without quotes and parentheses

Question

I am learning JavaScript and I have learned recently about JavaScript timing events  When I learned about setTimeout at W3Schools  I noticed a strange figure which I didn   t run into before  They are using double quotes and then call the function   Example    setTimeout  alertMsg     3000     I know that double and single quotes in JavaScript means a string   Also I saw that I can do the same like that   setTimeout alertMsg  3000     With the parentheses it   s referring  without the parentheses it   s copied  When I am using the quotes and the parentheses it   s getting crazy   I will be glad if someone can explain to me the difference between these three ways of using setTimeout   With the parentheses   setTimeout  alertMsg     3000     Without the quotes and the parentheses    setTimeout alertMsg  3000     And the third is only using quotes    setTimeout  alertMsg   3000       N B   A better source for setTimeout reference would be MDN

User · Answer

What happens in reality in case you pass string as a first parameter of function

setTimeout('string',number)

is value of first param got evaluated when it is time to run (after numberof miliseconds passed). Basically it is equal to

setTimeout(eval('string'), number)

This is

an alternative syntax that allows you to include a string instead of a function, which is compiled and executed when the timer expires. This syntax is not recommended for the same reasons that make using eval() a security risk.

So samples which you refer are not good samples, and may be given in different context or just simple typo.

If you invoke like this setTimeout(something, number), first parameter is not string, but pointer to a something called something. And again if something is string - then it will be evaluated. But if it is function, then function will be executed. jsbin sample

User · Answer

With the parentheses   setTimeout  alertMsg     3000      It work  here it treat as a function   Without the quotes and the parentheses   setTimeout alertMsg  3000      It also work  here it treat as a function   And the third is only using quotes   setTimeout  alertMsg   3000      It not work  here it treat as a string    x000D   x000D  function alertMsg1     x000D          alert  message 1    x000D        x000D      function alertMsg2     x000D          alert  message 2    x000D        x000D      function alertMsg3     x000D          alert  message 3    x000D        x000D      function alertMsg4     x000D          alert  message 4    x000D        x000D   x000D         this work after 2 second x000D      setTimeout alertMsg1  2000   x000D   x000D         This work immediately x000D      setTimeout alertMsg2    4000   x000D   x000D         this fail x000D      setTimeout  alertMsg3   6000   x000D   x000D         this work after 8second x000D      setTimeout  alertMsg4     8000   x000D   x000D   x000D       In the above example first alertMsg2   function call immediately  we   give the time out 4S but it don t bother  after that alertMsg1    A   time wait of 2 Second  then alertMsg4    A time wait of 8 Second  but   the alertMsg3   is not working because we place it within the quotes   without parties so it is treated as a string

User · Answer

If i want to wait for some response from server or any action we use setTimeOut       functionOne  function        console info  First         setTimeout     gt       console info  After timeOut 1          5000       console info  only setTimeOut   inside code waiting                 functionTwo  function        console info  second              functionOne        functionTwo        So here console info  After timeOut 1    will be executed after time elapsed  Output                                                                                   First only setTimeOut   inside code waiting   second undefined After timeOut 1     executed after time elapsed

User · Answer

Using setInterval or setTimeout  You should pass a reference to a function as the first argument for setTimeout or setInterval  This reference may be in the form of    An anonymous function  setTimeout function      Look mah  No name      2000    A name of an existing function   function foo         setTimeout foo  2000    A variable that points to an existing function  var foo   function          setTimeout foo  2000     Do note that I set  variable in a function  separately from  function name   It s not apparent that variables and function names occupy the same namespace and can clobber each other    Passing arguments  To call a function and pass parameters  you can call the function inside the callback assigned to the timer   setTimeout function      foo arg1  arg2     argN      1000     There is another method to pass in arguments into the handler  however it s not cross-browser compatible   setTimeout foo  2000  arg1  arg2     argN     Callback context  By default  the context of the callback  the value of this inside the function called by the timer  when executed is the global object window  Should you want to change it  use bind   setTimeout function      this     YOUR CONTEXT     true   bind YOUR CONTEXT   2000     Security  Although it s possible  you should not pass a string to setTimeout or setInterval  Passing a string makes setTimeout   or setInterval   use a functionality similar to eval   that executes strings as scripts  making arbitrary and potentially harmful script execution possible

User · Answer

Totally agree with Joseph   Here is a fiddle to test this  http   jsfiddle net nicocube 63s2s   In the context of the fiddle  the string argument do not work  in my opinion because the function is not defined in the global scope

User · Answer

i think the setTimeout function that you write is not being run  if you use jquery  you can make it run correctly by doing this         function alertMsg             your func              document  ready function            setTimeout alertMsg 3000              the function you called by setTimeout must not be a string

[javascript] Difference between setTimeout with and without quotes and parentheses

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