Is there any way to disable "groupSeparator"

[Argun]

The default groupSeparator is "," Is there any way to disable groupSeparator? I change the groupSeparator to empty string but it doesn't work.

[MikeMcl]

You can either set groupSeparator to the empty string or set groupSize to zero.

I suspect you are trying

BigNumber.set({FORMAT: {groupSeparator: ''})

but that will mean that the values for the other format properties are lost. To avoid this, even if you want to change only one format property, an object with all the format properties you need must be passed.

Alternatively, change individual properties by using a reference to the passed format object as shown below.

// default values
format = {
  decimalSeparator: '.',
  groupSeparator: ',',
  groupSize: 3,
  secondaryGroupSize: 0,
  fractionGroupSeparator: ' ',
  fractionGroupSize: 0
}
BigNumber.set({ FORMAT: format })

x = new BigNumber('123456789.123456789')
x.toFormat()                    // '123,456,789.123456789'

format.groupSeparator = ''
x.toFormat()                    // '123456789.123456789'

format.groupSeparator = ','
x.toFormat()                    // '123,456,789.123456789'

format.groupSize = 0
x.toFormat()                    // '123456789.123456789'

See toFormat.