Javascript setInterval not working

Question

I need to run a javascript function each 10 seconds   I understand the syntax must work like follow but I am not getting any success   function funcName         alert  test       var func   funcName    var run   setInterval  func  10000    But this isn t working  Any help

User · Answer

Change setInterval  func  10000  to either setInterval funcName  10000  or setInterval  funcName    10000   The former is the recommended method

User · Answer

Try this   function funcName         alert  test       var run   setInterval funcName  10000

User · Answer

That s because you should pass a function  not a string   function funcName         alert  test       setInterval funcName  10000     Your code has two problems    var func   funcName    calls the function immediately and assigns the return value  Just  func  is invalid even if you use the bad and deprecated eval-like syntax of setInterval  It would be setInterval  func     10000  to call the function eval-like

User · Answer

A lot of other answers are focusing on a pattern that does work  but their explanations aren t really very thorough as to why your current code doesn t work   Your code  for reference   function funcName         alert  test       var func   funcName    var run   setInterval  func  10000    Let s break this up into chunks  Your function funcName is fine  Note that when you call funcName  in other words  you run it  you will be alerting  test   But notice that funcName   -- the parentheses mean to  call  or  run  the function -- doesn t actually return a value  When a function doesn t have a return value  it defaults to a value known as undefined    When you call a function  you append its argument list to the end in parentheses  When you don t have any arguments to pass the function  you just add empty parentheses  like funcName    But when you want to refer to the function itself  and not call it  you don t need the parentheses because the parentheses indicate to run it    So  when you say   var func   funcName      You are actually declaring a variable func that has a value of funcName    But notice the parentheses  funcName   is actually the return value of funcName  As I said above  since funcName doesn t actually return any value  it defaults to undefined  So  in other words  your variable func actually will have the value undefined    Then you have this line   var run   setInterval  func  10000    The function setInterval takes two arguments  The first is the function to be ran every so often  and the second is the number of milliseconds between each time the function is ran    However  the first argument really should be a function  not a string  If it is a string  then the JavaScript engine will use eval on that string instead  So  in other words  your setInterval is running the following JavaScript code   func    10 seconds later     func    and so on   However  func is just a variable  with the value undefined  but that s sort of irrelevant   So every ten seconds  the JS engine evaluates the variable func and returns undefined  But this doesn t really do anything  I mean  it technically is being evaluated every 10 seconds  but you re not going to see any effects from that    The solution is to give setInterval a function to run instead of a string  So  in this case   var run   setInterval funcName  10000     Notice that I didn t give it func  This is because func is not a function in your code  it s the value undefined  because you assigned it funcName    Like I said above  funcName   will call the function funcName and return the return value of the function  Since funcName doesn t return anything  this defaults to undefined  I know I ve said that several times now  but it really is a very important concept  when you see funcName    you should think  the return value of funcName   When you want to refer to a function itself  like a separate entity  you should leave off the parentheses so you don t call it  funcName   So  another solution for your code would be   var func   funcName  var run   setInterval func  10000     However  that s a bit redundant  why use func instead of funcName    Or you can stay as true as possible to the original code by modifying two bits   var func   funcName  var run   setInterval  func     10000     In this case  the JS engine will evaluate func   every ten seconds  In other words  it will alert  test  every ten seconds  However  as the famous phrase goes  eval is evil  so you should try to avoid it whenever possible   Another twist on this code is to use an anonymous function  In other words  a function that doesn t have a name -- you just drop it in the code because you don t care what it s called   setInterval function          alert  test       10000     In this case  since I don t care what the function is called  I just leave a generic  unnamed  anonymous  function there

[javascript] Javascript setInterval not working

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