"breakOn is not defined" after the snippet is run during a breakpoint

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If, while the debugger is paused at a breakpoint, I decide to use breakOn() and run the snippet that defines it, then I get "breakOn is not defined" when I try to use it.

It seems that the first line should be

breakOn = function(obj, propertyName, mode, func) {

instead of

function breakOn(obj, propertyName, mode, func) {

See this thread and its old long version.