While variable is not defined - wait

Question

I have a click event that is triggered from another place automatically for the first time  My problem is that it runs too soon  since the required variables are still being defined by Flash and web services  So right now I have    function             window  load function            setTimeout function                   a play   trigger  click               5000              jQuery     The problem is that 5 seconds for a person with a slow internet connection could be too fast and vice versa  for a person with a fast internet connection  it s too slow   So how should I do the delay or timeout until someVariable is defined

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Object defineProperty window   propertyName         set  value   gt            this  value   value             someAction               get       gt  this  value       or even if you just want this property to be passed as an argument to a function and don t need it to be defined on a global object   Object defineProperty window   propertyName     set  value   gt  someAction value       However  since in your example you seem to want to perform an action upon creation of a node  I would suggest you take a look at MutationObservers

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You could have Flash call the function when it s done  I m not sure what you mean by web services  I assume you have JavaScript code calling web services via Ajax  in which case you would know when they terminate  In the worst case  you could do a looping setTimeout that would check every 100 nbsp ms or so   And the check for whether or not a variable is defined can be just if  myVariable  or safer  if typeof myVariable     undefined

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async  await implementation  improvement over  Toprak s answer  async     gt        console log  quot waiting for variable quot        while  window hasOwnProperty  quot myVar quot       define the condition as you like         await new Promise resolve   gt  setTimeout resolve  1000        console log  quot variable is defined quot          console log  quot above code doesn t block main function stack quot      After revisiting the OP s question  There is actually a better way to implement what was intended   quot variable set callback quot   Although the below code only works if the desired variable is encapsulated by an object  or window  instead of declared by let or var  I left the first answer because I was just doing improvement over existing answers without actually reading the original question   let obj   encapsulatedObject    window  Object defineProperty obj   quot myVar quot         configurable  true      set v           Object defineProperty obj   quot myVar quot                 configurable  true  enumerable  true  writable  true  value  v             console log  quot window myVar is defined quot                    see Object defineProperty or use es6 proxy  which is probably overkill   If you are looking for more   x000D   x000D         combining the two as suggested by  Emmanuel Mahuni     and showing an alternative to handle defineProperty setter and getter       let obj         window   async     gt      let  foo   await new Promise res   gt        Object defineProperty obj   foo     set  res             console log  obj foo is defined with value     foo            IMPORTANT  note that obj foo is still undefined the reason is out of scope of this question answer take a research of Object defineProperty to see more        TEST CODE  console log  test start    setTimeout async      gt      console log  about to assign obj foo      obj foo    Hello World         try uncomment the following line and compare the output      await new Promise res   gt  setTimeout res      console log  finished assigning obj foo      console log  value of obj foo    obj foo      undefined      console  obj foo is defined with value  Hello World     2000   x000D   x000D   x000D

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Instead of using the windows load event use the ready event on the document     document  ready function              This should fire when everything in the DOM is ready to go  including media content fully loaded

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Shorter way      var queue   function  args         typeof variableToCheck      undefined   doSomething args    setTimeout function     queue args    2000        You can also pass arguments

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I have upvoted  dnuttle s answer  but ended up using the following strategy      On doc ready for modern browsers document addEventListener  DOMContentLoaded    e    gt         Scope all logic related to what you want to achieve by using a function   const waitForMyFunction        gt           Use a timeout id to identify your process and purge it when it s no longer needed     let timeoutID         Check if your function is defined  in this case by checking its type     if  typeof myFunction      function              We no longer need to wait  purge the timeout id       window clearTimeout timeoutID             myFunction  is defined  invoke it with parameters  if any       myFunction  param1    param2          else             myFunction  is undefined  try again in 0 25 secs       timeoutID   window setTimeout waitForMyFunction  250                   Initialize   waitForMyFunction          It is tested and working      Gist  https   gist github com dreamyguy f319f0b2bffb1f812cf8b7cae4abb47c

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The following will keep looking for someVariable until it is found   It checks every 0 25 seconds   function waitForElement        if typeof someVariable      undefined              variable exists  do what you want           else          setTimeout waitForElement  250

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Very late to the party but I want to supply a more modern solution to any future developers looking at this question  It s based off of Toprak s answer but simplified to make it clearer as to what is happening   lt div gt Result   lt span id  quot result quot  gt  lt  span gt  lt  div gt    lt script gt      var output   null              Define an asynchronous function which will not block where it is called      async function test               Create a promise with the await operator which instructs the async function to wait for the promise to complete          await new Promise function resolve  reject                  Execute the code that needs to be completed                 In this case it is a timeout that takes 2 seconds before returning a result               setTimeout function                       Just call resolve   with the result wherever the code completes                  resolve  quot success output quot                   2000                               Just for reference  an  error  has been included                 It has a chance to occur before resolve   is called in this case  but normally it would only be used when your code fails              setTimeout function                       Use reject   if your code isn t successful                  reject  quot error output quot                   Math random     4000                       then function result                   The result variable comes from the first argument of resolve                output   result                       catch function error                   The error variable comes from the first argument of reject                   Catch will also catch any unexpected errors that occur during execution                 In this case  the output variable will be set to either of those results              if  error  output   error                                   Set the content of the result span to output after the promise returns          document querySelector  quot  result quot   innerHTML   output                    Execute the test async function      test            Executes immediately after test is called      document querySelector  quot  result quot   innerHTML    quot nothing yet quot    lt  script gt   Here s the code without comments for easy visual understanding  var output   null   async function test        await new Promise function resolve  reject           setTimeout function                resolve  quot success output quot               2000            setTimeout function                reject  quot error output quot               Math random     4000               then function result            output   result               catch function error            if  error  output   error                document querySelector  quot  result quot   innerHTML   output     test     document querySelector  quot  result quot   innerHTML    quot nothing yet quot    On a final note  according to MDN  Promises are supported on all modern browsers with Internet Explorer being the only exception  This compatibility information is also supported by caniuse  However with Bootstrap 5 dropping support for Internet Explorer  and the new Edge based on webkit  it is unlikely to be an issue for most developers

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I prefer something simple like this   function waitFor variable  callback      var interval   setInterval function         if  window variable           clearInterval interval         callback               200       And then to use it with your example variable of someVariable   waitFor  someVariable   function          do something here now that someVariable is defined       Note that there are various tweaks you can do  In the above setInterval call  I ve passed 200 as how often the interval function should run  There is also an inherent delay of that amount of time   200ms  before the variable is checked for -- in some cases  it s nice to check for it right away so there is no delay

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With Ecma Script 2017 You can use async-await and while together to do that And while will not crash or lock the program even variable never be true   x000D   x000D    First define some delay function which is called from async function x000D  function   delay   timer    x000D      return new Promise resolve   gt    x000D          timer   timer    2000  x000D          setTimeout function      x000D              resolve    x000D             timer   x000D          x000D     x000D   x000D    Then Declare Some Variable Global or In Scope x000D    Depends on you x000D  let Variable   false  x000D   x000D    And define what ever you want with async fuction x000D  async function some     x000D      while   Variable  x000D          await   delay   1000   x000D   x000D           code here because when Variable   true this function will x000D     x000D                                                               x000D    In Your Case x000D    1 Define Global Variable For Check Statement x000D    2 Convert function to async like below x000D   x000D  var isContinue   false  x000D  setTimeout async function      x000D        STOPT THE FUNCTION UNTIL CONDITION IS CORRECT x000D      while   isContinue  x000D          await   delay   1000   x000D   x000D        WHEN CONDITION IS CORRECT THEN TRIGGER WILL CLICKED x000D         a play   trigger  click    x000D     1   x000D                                                                x000D   x000D   x000D    Also you don t have to use setTimeout in this case just make ready function asynchronous

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You can use this   var refreshIntervalId   null  refreshIntervalId   setInterval checkIfVariableIsSet  1000    var checkIfVariableIsSet   function         if typeof someVariable      undefined               a play   trigger  click            clearInterval refreshIntervalId

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Here s an example where all the logic for waiting until the variable is set gets deferred to a function which then invokes a callback that does everything else the program needs to do - if you need to load variables before doing anything else  this feels like a neat-ish way to do it  so you re separating the variable loading from everything else  while still ensuring  everything else  is essentially a callback   var loadUser   function everythingElse       var interval   setInterval function          if typeof CurrentUser name      undefined             scope username   CurrentUser name          clearInterval interval           everythingElse                  1           loadUser function           everything else

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I would prefer this code   function checkVariable         if  variableLoaded    true              Here is your next action           setTimeout checkVariable  1000

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