Document.queryCommandEnabled()
Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
  The Document.queryCommandEnabled() method reports whether
  or not the specified editor command is enabled by the browser.
Syntax
isEnabled = document.queryCommandEnabled(command);
Parameters
command- 
    
The command for which to determine support.
 
Return value
  Returns a boolean value which is true if the command is enabled
  and false if the command isn't.
Notes
- 
    For '
cut' and 'copy' commands the method only returns true when called from a user-initiated thread. - 
    The 
'paste'command returnfalsenot only if the feature is unavailable, but also if the script calling it has insufficient privileges to perform the action. 
Example
var flg = document.queryCommandEnabled("SelectAll");
if(flg) {
  document.execCommand("SelectAll", false, null); // command is enabled, run it
}
Specifications
This feature is not part of any current specification. It is no longer on track to become a standard.
Browser compatibility
BCD tables only load in the browser