How would the world react if Russia launched a nuclear attack?

I am neither a military critic nor a politician. People with similar titles say Russia's economic sanctions should not be taken lightly because they are worried about Russia's nuclear attack.

Is that so?

Russia’s assault on Ukraine and its veiled threats of using nuclear arms have policymakers, past and present, thinking the unthinkable: How should Japanese respond to a Russian battlefield explosion of a nuclear bomb?

In such an attack, short range, lower yield ‘battlefield’ nuclear weapons – of which there are thought to be more than 1,000 in reserve – would be the most likely used.
Ukraine or other countries open to nuclear weapons explosions with the possibility of hundreds of thousand dead, depending on the target. Of course, Japan too. 

If Russia were to attack Ukraine with nuclear weapons, NATO countries would most likely respond on the grounds that the impact of nuclear weapons crosses borders and affects the countries surrounding Ukraine. 
NATO could respond either by using conventional forces on Russian strategic assets, or respond in kind using nuclear weapons as it has several options available. The US has around 150 B-61 nuclear gravity bombs stationed in five NATO countries – Belgium, Germany, the Netherlands, Italy, and Turkey – and the US, UK, and France also have long range capability for nuclear attacks under NATO auspices.

It is always possible – although assumed to be highly unlikely – that Putin may decide to launch a long-range ballistic missile attack against the US, but he knows – as do all his officials – that this would be the end of Russia.

In my opinion, it would be wise to think that Japan can curb attacks from Russia by cooperating with NATO countries, rather than receiving a nuclear attack without doing anything.