Yes Array.forEach is synchronous but be careful when you write async code inside forEach function body.

Array.forEach_is_synchronous.js

var fs = require('fs');

fs.readFile('users.json',function(err,data){
	var users = JSON.parse(data).results.slice(0,100);
	console.log("Users "+users.length);

	users.forEach(function(user,index){
        var prefix = index+1;
		   fs.writeFile('users/user_'+prefix+'.json',JSON.stringify(user),function(err){
		   	if(err){
			  	console.log("Error "+err)
			  }
			  else{
			  	console.log(prefix + " writing done")
			  }
	   	})
		console.log(prefix + " done")
	})
});