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Javascript TesterJavascript Tester

Javascript tester - online javascript tester for editing and testing your javascript code snippets.

Use the javascript tester to quickly test your javascript functions and code. For more complex testing of code/html/css use something like CodePen or JSFiddle.

The javascript tester will highlight syntax errors in the editor and provide meaningful messages to help debug your code. Runtime errors are shown below the editor.

Result of evaluating code:


The tester will evaluate your code and print the result to result section under the editor. The basic idea is you enter snippets of code you want to test with. The last expression will get printed as a result. The last expression should not contain a "return" statement or a variable assignment. It should just be an expression. You can also add additional console.log messages at various points in you code and these will also be shown in the result section on this page.

For example:

const dogs = [
      {age: 10, name: 'Fido'}, 
      {age: 14, name: 'Bowser'},
      {age: 16, name: 'Rusty'}
    ]; =>;        
Try adding the following before the last statement and then click Run again:
console.log( => {return {name:}}));

Great for testing ideas or running simple code snippets...

This editor works entirely in your browser (it uses the Ace embeddable code editor.). Your code is not sent to any server. If you close the browser or tab the current state of the edior is saved. If you don't want you code saved remember to clear the editor before closing. We value Privacy!

See below for keyboard shortcuts


  • Syntax highlighting
  • Automatic indent and outdent
  • Live syntax checking
  • Handles large documents
  • Search and replace with regular expressions (Ctrl-F)
  • Highlight matching parentheses
  • Drag and drop text using the mouse
  • Line wrapping
  • Code folding
  • Multiple cursors and selections
  • Cut, copy, and paste functionality

The following video gives some color theory basics to help you with your selections.

Editor Keyboard Shortcuts

Line Operations

Windows/Linux Mac Action
Ctrl-D Command-D Remove line
Alt-Shift-Down Command-Option-Down Copy lines down
Alt-Shift-Up Command-Option-Up Copy lines up
Alt-Down Option-Down Move lines down
Alt-Up Option-Up Move lines up
Alt-Delete Ctrl-K Remove to line end
Alt-Backspace Command-Backspace Remove to linestart
Ctrl-Backspace Option-Backspace, Ctrl-Option-Backspace Remove word left
Ctrl-Delete Option-Delete Remove word right
Ctrl-O Split line


Windows/Linux Mac Action
Ctrl-A Command-A Select all
Shift-Left Shift-Left Select left
Shift-Right Shift-Right Select right
Ctrl-Shift-Left Option-Shift-Left Select word left
Ctrl-Shift-Right Option-Shift-Right Select word right
Shift-Home Shift-Home Select line start
Shift-End Shift-End Select line end
Alt-Shift-Right Command-Shift-Right Select to line end
Alt-Shift-Left Command-Shift-Left Select to line start
Shift-Up Shift-Up Select up
Shift-Down Shift-Down Select down
Shift-PageUp Shift-PageUp Select page up
Shift-PageDown Shift-PageDown Select page down
Ctrl-Shift-Home Command-Shift-Up Select to start
Ctrl-Shift-End Command-Shift-Down Select to end
Ctrl-Shift-D Command-Shift-D Duplicate selection
Ctrl-Shift-P Select to matching bracket


Windows/Linux Mac Action
Ctrl-Alt-Up Ctrl-Option-Up Add multi-cursor above
Ctrl-Alt-Down Ctrl-Option-Down Add multi-cursor below
Ctrl-Alt-Right Ctrl-Option-Right Add next occurrence to multi-selection
Ctrl-Alt-Left Ctrl-Option-Left Add previous occurrence to multi-selection
Ctrl-Alt-Shift-Up Ctrl-Option-Shift-Up Move multicursor from current line to the line above
Ctrl-Alt-Shift-Down Ctrl-Option-Shift-Down Move multicursor from current line to the line below
Ctrl-Alt-Shift-Right Ctrl-Option-Shift-Right Remove current occurrence from multi-selection and move to next
Ctrl-Alt-Shift-Left Ctrl-Option-Shift-Left Remove current occurrence from multi-selection and move to previous
Ctrl-Shift-L Ctrl-Shift-L Select all from multi-selection

Go to

Windows/Linux Mac Action
Left Left, Ctrl-B Go to left
Right Right, Ctrl-F Go to right
Ctrl-Left Option-Left Go to word left
Ctrl-Right Option-Right Go to word right
Up Up, Ctrl-P Go line up
Down Down, Ctrl-N Go line down
Alt-Left, Home Command-Left, Home, Ctrl-A Go to line start
Alt-Right, End Command-Right, End, Ctrl-E Go to line end
PageUp Option-PageUp Go to page up
PageDown Option-PageDown, Ctrl-V Go to page down
Ctrl-Home Command-Home, Command-Up Go to start
Ctrl-End Command-End, Command-Down Go to end
Ctrl-L Command-L Go to line
Ctrl-Down Command-Down Scroll line down
Ctrl-Up Scroll line up
Ctrl-P Go to matching bracket
Option-PageDown Scroll page down
Option-PageUp Scroll page up


Windows/Linux Mac Action
Ctrl-F Command-F Find
Ctrl-H Command-Option-F Replace
Ctrl-K Command-G Find next
Ctrl-Shift-K Command-Shift-G Find previous


Windows/Linux Mac Action
Alt-L, Ctrl-F1 Command-Option-L, Command-F1 Fold selection
Alt-Shift-L, Ctrl-Shift-F1 Command-Option-Shift-L, Command-Shift-F1 Unfold
Alt-0 Command-Option-0 Fold all
Alt-Shift-0 Command-Option-Shift-0 Unfold all


Windows/Linux Mac Action
Tab Tab Indent
Shift-Tab Shift-Tab Outdent
Ctrl-Z Command-Z Undo
Ctrl-Shift-Z, Ctrl-Y Command-Shift-Z, Command-Y Redo
Ctrl-, Command-, Show the settings menu
Ctrl-/ Command-/ Toggle comment
Ctrl-T Ctrl-T Transpose letters
Ctrl-Enter Command-Enter Enter full screen
Ctrl-Shift-U Ctrl-Shift-U Change to lower case
Ctrl-U Ctrl-U Change to upper case
Insert Insert Overwrite
Ctrl-Shift-E Command-Shift-E Macros replay
Ctrl-Alt-E Macros recording
Delete Delete
Ctrl-L Center selection