Is it possible to change javascript variable values while debugging in Google Chrome

Question

I m debugging a javascript app  using Chrome dev tools   and I would like to change some variable values while stepping through the code   Is that possible at all   I have tried and got something like    gt  modeline 1  gt  modeline 0 0              lt  lt  lt  seems to work but      gt  modeline 1              lt  lt  lt  ups     But I m unable to find any documentation that states what can or can t be done

User · Answer

I m able to modify a script variable value by assignment in the Console   Seems simplest

User · Answer

Actually there is a workaround   Copy the entire method  modify it s name  e g  originalName   to originalName2   but modify the variable inside to take on whatever value you want  or pass it in as a parameter     Then if you call this method directly from the console  it will have the same functionality but you will be able to modify the variable values   If the method is called automatically then instead type into the console  originalName   null  function originalName original params          alert  modified internals        add whatever original code you want

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I was having the same issue  went to the  About Google Chrome - Help and it said I needed to restart my browser to get the latest updates   I did this  and suddenly  I can now change local variables  Simply click the variable you want to edit in the Scope Variables window  and type in your new value   I did notice some oddities though  that I had to step over some unrelated var assignments before I could alter the text in the right hand window  Scope Variables

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Why is this answer still getting upvotes   Per Mika  l Mayer s answer  this is no longer a problem  and my answer is obsolete  go   now returns 30 after mucking with the console    This was fixed in July 2013  according to the bug report linked above in gabrielmaldi s comment   It alarms me that I m still getting upvotes - makes me think the upvoter doesn t understand either the question or my answer   I ll leave my original answer here for historical reasons  but go upvote Mika  l s answer instead     The trick is that you can t change a local variable directly  but you can modify the properties of an object   You can also modify the value of a global variable   var g n   0  function go         var n   0      var o     n  0        return g n   n   o n      breakpoint here     console    gt  g n   10   10  gt  g n   10  gt  n   10   10  gt  n   0  gt  o n   10   10  gt  o n   10   Check the result of go   after setting the breakpoint and running those calls in the console  and you ll find that the result is 20  rather than 0  but sadly  not 30

User · Answer

To modify a value every time a block of code runs without having to break execution flow  The  quot Logpoints quot  feature in the debugger is designed to let you log arbitrary values to the console without breaking  It evaluates code inside the flow of execution  which means you can actually use it to change values on the fly without stopping  Right-click a line number and choose  quot Logpoint  quot  then enter the assignment expression  It looks something like this   I find it super useful for setting values to a state not otherwise easy to reproduce  without having to rebuild my project with debug lines in it  REMEMBER to delete the breakpoint when you re done

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This is now possible in chrome 35  today as of July 11  2014   I don t know which version allowed it first though   Just tested  gilly3 example on my machine and it works    Open the console  in Sources and the tab Snippets  add a new snippet  paste the following code into it   var g n   0  function go         var n   0      var o     n  0        return g n   n   o n      breakpoint here   Right-click the snippet name  click  Run   this does not fire the function though  Add the breakpoint at the return statement  In the console below  type go   and change the variable values as  demonstrated below     and the returned result g n   n   o n is 30

User · Answer

It looks like not   Put a breakpoint  when it stops switch to the console  try to set the variable  It does not error when you assign it a different value  but if you read it after the assignment  it s unmodified   -

User · Answer

I don t know why chrome team don t allow this silly feature     but the only way I could change variable values with success is to modify the script directly in the chrome editor under  Sources  Tab  this changes the behavior of your script until you refresh the page   but that changes will lost when refresh  so be carefull

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This is an acknowledged bug in the Chrome Dev Tools   http   code google com p chromium issues detail id 124206

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Firebug seems to allow you to do that

User · Answer

Yes  Finally  I just tried it with Chrome  Version 66 0 3359 170  Official Build   64-bit  on Mac   You can change the values in the scopes as in the first picture  or with the console as in the second picture

[javascript] Is it possible to change javascript variable values while debugging in Google Chrome?

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